BSC NURSING SEM1 APPLIED ANATOMY UNIT10The Nervous system
Review Structure of neurons
Structure of Neurons
A neuron is the fundamental unit of the nervous system, responsible for transmitting and processing information through electrical and chemical signals. Neurons have specialized structures for receiving, integrating, and sending signals.
1. Parts of a Neuron
a. Cell Body (Soma)
Structure:
Contains the nucleus (with DNA) and organelles like mitochondria, Golgi apparatus, and rough endoplasmic reticulum (RER).
The RER in neurons is called Nissl bodies, involved in protein synthesis.
Function:
Maintains cellular functions.
Processes input from dendrites and integrates signals.
b. Dendrites
Structure:
Short, branching projections extending from the cell body.
Contain receptors for neurotransmitters.
Function:
Receive signals (electrical or chemical) from other neurons or sensory receptors.
Transmit signals toward the cell body.
c. Axon
Structure:
A single, elongated projection that extends from the cell body.
Originates at the axon hillock, where action potentials are generated.
May be covered with myelin sheath for faster signal conduction.
Ends in axon terminals (synaptic knobs), which contain vesicles filled with neurotransmitters.
Function:
Transmits signals away from the cell body to other neurons, muscles, or glands.
d. Myelin Sheath
Structure:
A fatty, insulating layer formed by:
Schwann cells in the peripheral nervous system (PNS).
Oligodendrocytes in the central nervous system (CNS).
Gaps in the sheath are called Nodes of Ranvier.
Function:
Increases the speed of signal conduction through saltatory conduction.
e. Nodes of Ranvier
Structure:
Gaps in the myelin sheath along the axon.
Function:
Facilitate rapid signal conduction by allowing the action potential to “jump” from node to node.
f. Axon Terminals (Synaptic Knobs)
Structure:
The ends of the axon, containing synaptic vesicles filled with neurotransmitters.
Function:
Release neurotransmitters into the synaptic cleft to communicate with other neurons, muscles, or glands.
2. Types of Neurons Based on Structure
Multipolar Neurons:
Structure: One axon and multiple dendrites.
Location: Found in the CNS (e.g., motor neurons).
Function: Integrate information and send motor commands.
Bipolar Neurons:
Structure: One axon and one dendrite.
Location: Found in sensory organs (e.g., retina of the eye, olfactory system).
Function: Specialized for sensory input.
Unipolar (Pseudounipolar) Neurons:
Structure: A single process splits into a peripheral branch (dendrite) and a central branch (axon).
Location: Found in sensory neurons of the PNS (e.g., dorsal root ganglia).
Function: Transmit sensory information.
Anaxonic Neurons:
Structure: No distinct axon; only dendrites.
Location: Found in the brain and retina.
Function: Play a role in signal processing.
3. Types of Neurons Based on Function
Sensory (Afferent) Neurons:
Transmit signals from sensory receptors to the CNS.
Example: Touch, pain, temperature.
Motor (Efferent) Neurons:
Transmit signals from the CNS to muscles or glands.
Example: Stimulating muscle contraction.
Interneurons:
Found only in the CNS; connect sensory and motor neurons.
Example: Reflex arcs.
4. Synapse
Structure:
Presynaptic Neuron:
The neuron that sends the signal.
Synaptic Cleft:
The gap between the presynaptic and postsynaptic neuron.
Postsynaptic Neuron:
The neuron that receives the signal.
Function:
The synapse facilitates communication between neurons using neurotransmitters.
Summary Table: Structure and Function of a Neuron
Part
Structure
Function
Cell Body (Soma)
Contains nucleus and organelles
Maintains the neuron and integrates signals.
Dendrites
Branching extensions from the soma
Receive signals and transmit them to the soma.
Axon
Long, singular projection
Transmits signals away from the soma.
Myelin Sheath
Insulating fatty layer around axon
Increases signal conduction speed.
Nodes of Ranvier
Gaps in the myelin sheath
Enable saltatory conduction.
Axon Terminals
End of the axon
Release neurotransmitters for signal transfer.
Clinical Relevance
Multiple Sclerosis (MS):
Autoimmune disease where the myelin sheath in the CNS is damaged, slowing signal transmission.
Neuropathy:
Damage to peripheral nerves, causing sensory or motor dysfunction.
Neurodegenerative Disorders:
Diseases like Alzheimer’s and Parkinson’s involve neuron degeneration, leading to impaired signaling.
Reflex Arcs:
Neurons are essential for reflex actions, connecting sensory inputs to motor outputs.
CNS, ANS and PNS (Central, autonomic and peripheral)
CNS, ANS, and PNS: Overview
The nervous system is divided into the Central Nervous System (CNS), Peripheral Nervous System (PNS), and Autonomic Nervous System (ANS). Each plays a distinct role in sensory input, information processing, and response generation.
1. Central Nervous System (CNS)
Definition
The CNS consists of the brain and spinal cord, serving as the control center for processing and integrating information.
Components
Brain:
Controls higher-order functions like thought, memory, emotions, and voluntary movements.
Divided into:
Cerebrum: Responsible for sensory perception, voluntary motor functions, and cognition.
Autonomic Nervous System (ANS): Controls involuntary functions (detailed below).
Functions
Connection: Links the CNS to limbs, organs, and sensory structures.
Sensory Input: Delivers information to the CNS from the external and internal environments.
Motor Output: Executes commands from the CNS.
3. Autonomic Nervous System (ANS)
Definition
The ANS is a subdivision of the PNS that regulates involuntary functions like heart rate, digestion, and glandular activity. It operates below conscious control.
Divisions
Sympathetic Nervous System (SNS):
Activates the “fight or flight” response during stress.
Effects:
Increases heart rate and blood pressure.
Dilates bronchioles and pupils.
Inhibits digestion and salivation.
Parasympathetic Nervous System (PNS):
Promotes the “rest and digest” state for relaxation and energy conservation.
Effects:
Decreases heart rate.
Stimulates digestion and glandular activity.
Constricts pupils and bronchioles.
Enteric Nervous System (ENS):
Often considered part of the ANS.
Independently regulates gastrointestinal functions like motility and secretion.
Comparison of CNS, PNS, and ANS
Feature
CNS
PNS
ANS
Primary Role
Integration and control.
Connection between CNS and body.
Regulates involuntary functions.
Components
Brain and spinal cord.
Cranial and spinal nerves.
Sympathetic, parasympathetic, and enteric.
Control
Conscious and unconscious.
Conscious (somatic) and unconscious (ANS).
Entirely unconscious.
Functions
Processes and integrates data.
Delivers sensory input and motor output.
Regulates heart rate, digestion, etc.
Interconnection Between CNS, PNS, and ANS
CNS:
Acts as the control center, processing sensory input and generating motor commands.
Example: The brain interprets pain and sends signals for a reflexive withdrawal.
PNS:
Serves as the communication network, transmitting signals between the CNS and the body.
Example: A sensory nerve detects a hot surface and sends a signal to the CNS.
ANS:
Functions independently but is regulated by the CNS (hypothalamus, brainstem).
Example: The hypothalamus triggers sympathetic activation during stress.
Clinical Relevance
CNS Disorders:
Stroke: Disruption of blood flow to the brain, leading to neurological deficits.
Multiple Sclerosis: Damage to the myelin sheath in the CNS.
PNS Disorders:
Peripheral Neuropathy: Damage to peripheral nerves, causing weakness, numbness, or pain.
Guillain-Barré Syndrome: An autoimmune attack on the PNS.
ANS Disorders:
Autonomic Dysreflexia: Overactivation of the ANS in spinal cord injuries.
Postural Orthostatic Tachycardia Syndrome (POTS): Dysregulation of autonomic control over blood pressure and heart rate.
Structure of brain,
Structure of the Brain
The brain is the control center of the body, responsible for coordinating sensory input, motor output, and higher cognitive functions. It is composed of specialized regions and structures, each with distinct roles. The brain is part of the central nervous system (CNS) and is protected by the skull, meninges, and cerebrospinal fluid (CSF).
Major Divisions of the Brain
The brain is divided into three main parts:
Forebrain (Prosencephalon)
Midbrain (Mesencephalon)
Hindbrain (Rhombencephalon)
1. Forebrain
The forebrain includes the cerebrum, thalamus, hypothalamus, and limbic system. It is responsible for higher cognitive functions, sensory processing, and hormonal regulation.
a. Cerebrum
Structure:
The largest part of the brain, divided into two hemispheres (left and right).
Temporal Lobe: Hearing, memory, language comprehension.
Occipital Lobe: Vision processing.
Cerebral Cortex:
Outer layer of gray matter involved in higher brain functions.
Contains gyri (ridges) and sulci (grooves) that increase surface area.
White Matter:
Beneath the cortex, composed of myelinated axons connecting brain regions.
Functions:
Voluntary motor control.
Sensory processing.
Language, memory, and emotions.
b. Thalamus
Structure:
A paired structure located above the brainstem.
Functions:
Acts as a sensory relay center, transmitting information to the cerebral cortex.
c. Hypothalamus
Structure:
Located below the thalamus.
Functions:
Regulates homeostasis, including temperature, hunger, and thirst.
Controls the pituitary gland and the autonomic nervous system.
d. Limbic System
Structure:
Includes the hippocampus, amygdala, and parts of the thalamus and hypothalamus.
Functions:
Regulates emotions, memory, and motivation.
2. Midbrain
The midbrain connects the forebrain and hindbrain and is involved in motor control, vision, and hearing.
Structure:
Includes the tectum (superior and inferior colliculi) and tegmentum.
Functions:
Superior Colliculi: Visual reflexes.
Inferior Colliculi: Auditory reflexes.
Substantia Nigra: Involved in movement control; its degeneration leads to Parkinson’s disease.
3. Hindbrain
The hindbrain consists of the cerebellum, pons, and medulla oblongata. It controls vital autonomic functions and coordination.
a. Cerebellum
Structure:
Located at the back of the brain, beneath the occipital lobe.
Composed of two hemispheres with a central vermis.
Functions:
Coordinates voluntary movements.
Maintains posture and balance.
b. Pons
Structure:
Located between the midbrain and medulla.
Functions:
Connects the cerebellum to the brainstem.
Regulates breathing and relays sensory information.
c. Medulla Oblongata
Structure:
Lowest part of the brainstem, continuous with the spinal cord.
Functions:
Controls vital functions such as heart rate, blood pressure, and respiration.
Protective Structures
Skull:
The bony structure encasing the brain.
Meninges:
Three protective layers:
Dura Mater: Tough outer layer.
Arachnoid Mater: Middle layer with a web-like structure.
Pia Mater: Thin inner layer adhering to the brain.
Cerebrospinal Fluid (CSF):
Circulates in the subarachnoid space and ventricles.
Cushions the brain and maintains a stable environment.
Blood Supply
Arterial Supply:
Provided by the internal carotid arteries and vertebral arteries, forming the Circle of Willis.
Venous Drainage:
Drains through the dural venous sinuses into the internal jugular veins.
Summary Table: Brain Divisions
Division
Components
Functions
Forebrain
Cerebrum, Thalamus, Hypothalamus
Cognitive functions, sensory relay, homeostasis.
Midbrain
Tectum, Tegmentum, Substantia Nigra
Motor control, vision, hearing reflexes.
Hindbrain
Cerebellum, Pons, Medulla Oblongata
Autonomic functions, coordination, balance.
Clinical Relevance
Stroke:
Disruption of blood flow to the brain, causing neurological deficits.
Traumatic Brain Injury (TBI):
Damage to the brain from external trauma.
Neurodegenerative Diseases:
Alzheimer’s Disease: Affects memory and cognition.
Parkinson’s Disease: Involves the degeneration of the substantia nigra.
spinal cord,
Structure of the Spinal Cord
The spinal cord is a cylindrical structure of the central nervous system (CNS) that extends from the brainstem to the lower back. It serves as a communication highway between the brain and the rest of the body, relaying sensory information to the brain and motor commands to muscles.
Anatomy of the Spinal Cord
1. External Structure
Length and Location:
Extends from the medulla oblongata (at the base of the brain) to the level of the L1–L2 vertebrae in adults.
Enclosed within the vertebral column for protection.
Regions:
Divided into five regions:
Cervical (C1–C8)
Thoracic (T1–T12)
Lumbar (L1–L5)
Sacral (S1–S5)
Coccygeal (Co1)
Conus Medullaris:
The tapered end of the spinal cord at L1–L2.
Cauda Equina:
A bundle of spinal nerves that continue beyond the conus medullaris.
Filum Terminale:
A fibrous extension of the pia mater that anchors the spinal cord to the coccyx.
2. Internal Structure
The spinal cord is divided into gray matter (central) and white matter (peripheral).
Gray Matter:
H-shaped structure in the center, containing neuron cell bodies.
Regions:
Dorsal Horn: Receives sensory input.
Ventral Horn: Contains motor neurons.
Lateral Horn (only in thoracic and lumbar regions): Contains autonomic neurons.
White Matter:
Surrounds the gray matter and consists of myelinated axons.
Organized into ascending tracts (sensory) and descending tracts (motor).
Central Canal:
A small channel in the middle of the gray matter filled with cerebrospinal fluid (CSF).
Functions of the Spinal Cord
Relay Center:
Transmits sensory signals from the body to the brain via ascending tracts.
Transmits motor signals from the brain to the body via descending tracts.
Reflex Center:
Mediates reflexes, which are automatic, involuntary responses to stimuli.
Protective Features
Vertebral Column:
Surrounds and protects the spinal cord.
Meninges:
Three protective layers:
Dura Mater: Tough outer layer.
Arachnoid Mater: Web-like middle layer.
Pia Mater: Thin inner layer adhering to the spinal cord.
Cerebrospinal Fluid (CSF):
Circulates in the subarachnoid space, providing cushioning and nutrient exchange.
Spinal Nerves
Structure:
The spinal cord gives rise to 31 pairs of spinal nerves, each formed by the union of:
Dorsal Root: Contains sensory fibers.
Ventral Root: Contains motor fibers.
Function:
Spinal nerves carry mixed signals (both sensory and motor) to and from the body.
Dorsal Column: Fine touch, vibration, proprioception.
Descending (Motor) Tracts
Carry motor commands from the brain to the body.
Examples:
Corticospinal Tract: Voluntary motor control.
Reticulospinal Tract: Posture and muscle tone.
Clinical Relevance
Spinal Cord Injury (SCI):
Damage can result in paralysis or loss of sensation depending on the level and severity.
Quadriplegia: Injury at cervical levels.
Paraplegia: Injury at thoracic or lumbar levels.
Herniated Disc:
Compression of spinal nerves due to displacement of intervertebral discs.
Reflex Testing:
Used to assess spinal cord function.
Example: Patellar Reflex tests the L2–L4 segments.
Meningitis:
Inflammation of the meninges, affecting spinal cord function.
Summary Table
Structure
Description
Function
Gray Matter
Central H-shaped region containing neuron cell bodies
Processes sensory and motor information.
White Matter
Outer region with myelinated axons
Transmits signals to/from the brain.
Dorsal Horn
Posterior part of gray matter
Receives sensory input.
Ventral Horn
Anterior part of gray matter
Sends motor output to muscles.
Spinal Nerves
31 pairs of mixed nerves
Transmit sensory and motor signals.
Meninges
Three protective layers
Cushion and protect the spinal cord.
Cerebrospinal Fluid
Fluid in the central canal and subarachnoid space
Provides cushioning and nutrients.
cranial nerves,
Cranial Nerves: Overview
Cranial nerves are 12 paired nerves that emerge directly from the brain and brainstem, rather than from the spinal cord. They are responsible for sensory, motor, and autonomic functions in the head, neck, and some thoracic and abdominal organs.
Sensory: Sensations from thoracic and abdominal organs.
Motor: Controls muscles of the larynx and pharynx.
Parasympathetic: Regulates heart, lungs, and digestive tract.
Type: Mixed.
XI. Accessory Nerve
Function: Shoulder and neck movements.
Type: Motor.
Muscles Controlled: Trapezius and sternocleidomastoid.
XII. Hypoglossal Nerve
Function: Tongue movement for speech and swallowing.
Type: Motor.
Mnemonic for Function (Sensory, Motor, or Both)
Some Say Money Matters But My Brother Says Big Brains Matter More.
S: Sensory
M: Motor
B: Both (Mixed)
Clinical Relevance
Olfactory Nerve (I):
Damage causes anosmia (loss of smell).
Optic Nerve (II):
Damage leads to visual field defects (e.g., hemianopia).
Oculomotor, Trochlear, and Abducens (III, IV, VI):
Damage causes diplopia (double vision) and eye movement disorders.
Trigeminal Nerve (V):
Trigeminal Neuralgia: Severe facial pain.
Facial Nerve (VII):
Bell’s Palsy: Unilateral facial paralysis.
Vestibulocochlear Nerve (VIII):
Disorders cause hearing loss or vertigo.
Glossopharyngeal and Vagus Nerves (IX, X):
Damage affects swallowing and speech.
Accessory Nerve (XI):
Weakness in shoulder shrugging or head rotation.
Hypoglossal Nerve (XII):
Damage causes tongue deviation and difficulty in speech or swallowing.
spinal nerves,
Spinal Nerves: Overview
Spinal nerves are part of the Peripheral Nervous System (PNS) and connect the central nervous system (CNS) to the body. There are 31 pairs of spinal nerves, emerging from the spinal cord, and they are responsible for transmitting sensory, motor, and autonomic signals between the body and the CNS.
Structure of Spinal Nerves
1. Roots of Spinal Nerves
Each spinal nerve has two roots:
Dorsal Root (Sensory/Afferent):
Carries sensory information from the body to the spinal cord.
Contains the dorsal root ganglion, which houses sensory neuron cell bodies.
Ventral Root (Motor/Efferent):
Carries motor commands from the spinal cord to muscles and glands.
The dorsal and ventral roots merge to form a mixed spinal nerve that contains both sensory and motor fibers.
2. Branches of Spinal Nerves
After exiting the spinal column, each spinal nerve divides into:
Dorsal Ramus:
Supplies the skin and muscles of the back.
Ventral Ramus:
Supplies the skin and muscles of the front and sides of the body and forms major nerve plexuses.
Meningeal Branch:
Re-enters the spinal canal to innervate the meninges, vertebrae, and blood vessels.
Rami Communicantes:
Involved in autonomic functions, connecting spinal nerves to the sympathetic trunk.
Classification of Spinal Nerves
Region
Number of Nerves
Corresponding Vertebrae
Example
Cervical
8 pairs (C1–C8)
Above C1 to below C7
Phrenic nerve (C3–C5).
Thoracic
12 pairs (T1–T12)
Below each thoracic vertebra
Intercostal nerves.
Lumbar
5 pairs (L1–L5)
Below each lumbar vertebra
Femoral nerve (L2–L4).
Sacral
5 pairs (S1–S5)
Through sacral foramina
Sciatic nerve (L4–S3).
Coccygeal
1 pair (Co1)
Near coccyx
Supplies skin near the coccyx.
Major Plexuses of Spinal Nerves
Spinal nerves, particularly the ventral rami, form nerve plexuses in certain regions.
Cervical Plexus (C1–C4):
Supplies the skin and muscles of the neck, shoulder, and diaphragm.
Key Nerve: Phrenic Nerve (C3–C5) controls the diaphragm.
Brachial Plexus (C5–T1):
Supplies the skin and muscles of the upper limb.
Key Nerves:
Median Nerve: Supplies forearm and hand muscles.
Radial Nerve: Controls the triceps and extensors of the arm.
Ulnar Nerve: Supplies hand muscles.
Lumbar Plexus (L1–L4):
Supplies the skin and muscles of the lower abdomen, thigh, and groin.
Key Nerve: Femoral Nerve: Controls the quadriceps.
Sacral Plexus (L4–S4):
Supplies the buttocks, perineum, and lower limbs.
Key Nerve: Sciatic Nerve: Largest nerve in the body, supplies the lower leg and foot.
Coccygeal Plexus (S4–Co1):
Supplies a small area of skin near the coccyx.
Functions of Spinal Nerves
Type
Function
Sensory (Afferent)
Transmit sensory information (e.g., pain, temperature, touch) to the CNS.
Motor (Efferent)
Carry motor commands from the CNS to skeletal muscles.
Autonomic
Control involuntary functions like gland secretion and blood vessel constriction.
Clinical Relevance
Spinal Nerve Compression:
Herniated discs can compress spinal nerves, causing pain or weakness.
Example: Sciatica caused by compression of the sciatic nerve.
Reflex Testing:
Certain reflexes test the function of specific spinal nerves.
Example:
Patellar Reflex: Tests L2–L4.
Achilles Reflex: Tests S1–S2.
Dermatomes:
Areas of skin supplied by sensory fibers of a single spinal nerve.
Useful for diagnosing nerve damage.
Plexus Injuries:
Brachial Plexus Injury: Can cause weakness or paralysis in the arm.
Lumbar Plexus Injury: Can lead to issues with lower limb movement.
Dermatomes
Dermatomes are skin regions innervated by a single spinal nerve. They are clinically important for identifying nerve or spinal cord injuries.
Region
Key Dermatome Areas
Cervical
C2: Back of the head; C6: Thumb.
Thoracic
T4: Nipple; T10: Umbilicus.
Lumbar
L1: Groin; L5: Big toe.
Sacral
S1: Lateral foot; S5: Perianal area.
Summary Table: Spinal Nerves
Region
Number
Function
Associated Plexus
Cervical
8 pairs
Head, neck, diaphragm, upper limbs (partial).
Cervical, Brachial Plexus.
Thoracic
12 pairs
Chest, abdomen, intercostal muscles.
None (intercostal nerves).
Lumbar
5 pairs
Lower abdomen, thigh.
Lumbar Plexus.
Sacral
5 pairs
Buttocks, perineum, lower limbs.
Sacral Plexus.
Coccygeal
1 pair
Skin over the coccyx.
Coccygeal Plexus.
peripheral nerves,
Peripheral Nerves: Overview
The peripheral nerves are part of the Peripheral Nervous System (PNS), which connects the central nervous system (CNS) to the rest of the body. Peripheral nerves include cranial nerves and spinal nerves, transmitting sensory, motor, and autonomic signals.
Types of Peripheral Nerves
Peripheral nerves are classified based on their function:
Sensory Nerves (Afferent):
Carry sensory information from the body to the CNS.
Examples: Pain, temperature, touch, and proprioception.
Motor Nerves (Efferent):
Transmit motor commands from the CNS to muscles.
Examples: Voluntary movement of skeletal muscles.
Mixed Nerves:
Contain both sensory and motor fibers.
Most peripheral nerves are mixed.
Autonomic Nerves:
Control involuntary functions (e.g., heart rate, digestion).
Divided into:
Sympathetic nerves (fight or flight).
Parasympathetic nerves (rest and digest).
Structure of Peripheral Nerves
Epineurium:
Outer connective tissue sheath that encloses the entire nerve.
Perineurium:
Surrounds bundles of nerve fibers (fascicles).
Endoneurium:
Surrounds individual nerve fibers (axons).
Axon:
The functional unit of the nerve.
May be myelinated (fast conduction) or unmyelinated (slow conduction).
Cranial Nerves as Part of Peripheral Nerves
There are 12 pairs of cranial nerves, which are peripheral nerves connecting directly to the brain.
Examples:
Vagus nerve (X): Controls autonomic functions in thoracic and abdominal organs.
Facial nerve (VII): Controls facial expression and taste.
Spinal Nerves as Peripheral Nerves
There are 31 pairs of spinal nerves, which arise from the spinal cord.
These nerves exit the spinal column and branch into:
Dorsal rami: Supply the back.
Ventral rami: Supply the limbs and anterior trunk, forming plexuses.
Major Peripheral Nerve Plexuses
Cervical Plexus (C1–C4):
Key nerve: Phrenic Nerve (C3–C5).
Function: Innervates the diaphragm.
Brachial Plexus (C5–T1):
Key nerves:
Median Nerve: Forearm and hand muscles.
Radial Nerve: Extensors of the arm and forearm.
Ulnar Nerve: Fine motor control of the hand.
Function: Supplies the upper limbs.
Lumbar Plexus (L1–L4):
Key nerve: Femoral Nerve.
Function: Innervates the anterior thigh muscles.
Sacral Plexus (L4–S4):
Key nerve: Sciatic Nerve.
Function: Supplies the lower limbs.
Coccygeal Plexus (S4–Co1):
Function: Supplies skin over the coccyx.
Examples of Key Peripheral Nerves
Nerve
Source
Function
Phrenic Nerve
Cervical Plexus (C3–C5)
Controls the diaphragm (breathing).
Median Nerve
Brachial Plexus
Supplies forearm flexors, controls thumb muscles.
Ulnar Nerve
Brachial Plexus
Controls fine motor movements in the hand.
Sciatic Nerve
Sacral Plexus
Largest nerve; supplies lower limbs.
Femoral Nerve
Lumbar Plexus
Controls thigh muscles for hip flexion.
Functions of Peripheral Nerves
Function
Description
Sensory Input
Transmit sensory signals (pain, temperature, touch) to the CNS.
Damage to peripheral nerves causing pain, numbness, or weakness.
Common causes: Diabetes, infections, or trauma.
Carpal Tunnel Syndrome:
Compression of the median nerve at the wrist, causing hand pain and weakness.
Sciatica:
Compression or irritation of the sciatic nerve, leading to pain radiating down the leg.
Bell’s Palsy:
Temporary paralysis of the facial nerve (VII), causing facial drooping.
Guillain-Barré Syndrome:
Autoimmune attack on peripheral nerves, leading to weakness or paralysis.
Summary Table: Peripheral Nerves
Type
Examples
Function
Sensory Nerves
Cutaneous nerves for skin sensation.
Transmit sensory information to the CNS.
Motor Nerves
Radial nerve, femoral nerve.
Control skeletal muscles.
Mixed Nerves
Spinal nerves.
Carry both sensory and motor fibers.
Autonomic Nerves
Sympathetic and parasympathetic nerves.
Regulate involuntary functions.
functional areas of cerebral cortex
Functional Areas of the Cerebral Cortex
The cerebral cortex is the outermost layer of the brain and plays a critical role in sensory perception, voluntary motor control, language, memory, and higher cognitive functions. It is divided into lobes—frontal, parietal, temporal, and occipital—each containing specialized functional areas.
Classification of Functional Areas
Motor Areas:
Control voluntary muscle movements.
Sensory Areas:
Process sensory input from various parts of the body.
Association Areas:
Integrate sensory and motor information for complex functions like reasoning, language, and problem-solving.
Major Functional Areas of the Cerebral Cortex
1. Frontal Lobe
Primary Motor Cortex (Precentral Gyrus):
Location: Anterior to the central sulcus.
Function: Controls voluntary movements of specific body parts.
Clinical Note: Damage can cause paralysis of specific muscles (contralateral side).
Premotor Cortex:
Location: Anterior to the primary motor cortex.
Function: Coordinates learned motor skills and movements.
Supplementary Motor Area:
Location: Medial surface of the frontal lobe.
Function: Planning and execution of complex movements.
Broca’s Area:
Location: Inferior frontal gyrus (left hemisphere in most people).
Function: Controls motor aspects of speech production.
Clinical Note: Damage leads to Broca’s aphasia (difficulty speaking).
Prefrontal Cortex:
Location: Anterior portion of the frontal lobe.
Function: Involved in executive functions, decision-making, planning, and personality.
Clinical Note: Damage can cause impulsive behavior and impaired decision-making.
Clinical Note: Damage can result in loss of sensation (contralateral side).
Somatosensory Association Cortex:
Location: Posterior to the primary somatosensory cortex.
Function: Integrates sensory information to understand objects, textures, and shapes.
Posterior Parietal Cortex:
Function: Spatial awareness and attention.
Clinical Note: Damage can cause hemispatial neglect.
3. Temporal Lobe
Primary Auditory Cortex:
Location: Superior temporal gyrus.
Function: Processes auditory information.
Clinical Note: Damage can cause hearing loss or difficulty distinguishing sounds.
Wernicke’s Area:
Location: Posterior part of the superior temporal gyrus (left hemisphere in most people).
Function: Responsible for language comprehension.
Clinical Note: Damage leads to Wernicke’s aphasia (fluent but nonsensical speech).
Temporal Association Cortex:
Function: Involved in recognition of faces and objects (fusiform gyrus).
Hippocampus:
Function: Memory formation and spatial navigation.
4. Occipital Lobe
Primary Visual Cortex (V1):
Location: Posterior pole of the occipital lobe.
Function: Processes visual input from the retina.
Clinical Note: Damage causes cortical blindness.
Visual Association Areas:
Location: Surrounds the primary visual cortex.
Function: Interprets visual information (e.g., color, motion, depth).
Clinical Note: Damage can result in visual agnosia (inability to recognize objects).
5. Insular Cortex
Location: Deep within the lateral sulcus.
Function: Involved in taste, visceral sensations, and emotional processing.
6. Limbic Lobe
Components: Cingulate gyrus, hippocampus, and amygdala.
Function: Regulates emotions, memory, and behavior.
Functional Map of the Cerebral Cortex
Area
Location
Function
Primary Motor Cortex
Precentral gyrus (frontal lobe)
Voluntary motor control.
Primary Somatosensory Cortex
Postcentral gyrus (parietal lobe)
Sensory input (touch, temperature, pain).
Broca’s Area
Inferior frontal gyrus
Speech production.
Wernicke’s Area
Superior temporal gyrus
Language comprehension.
Primary Visual Cortex
Occipital lobe
Visual processing.
Primary Auditory Cortex
Superior temporal gyrus
Hearing.
Prefrontal Cortex
Frontal lobe
Planning, reasoning, decision-making.
Somatosensory Association Cortex
Parietal lobe
Integrates sensory information.
Visual Association Area
Occipital lobe
Interpretation of visual stimuli.
Temporal Association Area
Temporal lobe
Object and facial recognition, memory.
Clinical Relevance
Stroke:
Can cause loss of motor or sensory functions depending on the affected cortical area.
Aphasia:
Broca’s Aphasia: Impaired speech production.
Wernicke’s Aphasia: Impaired language comprehension.
Agnosia:
Inability to recognize objects (visual agnosia) or faces (prosopagnosia).
Seizures:
Temporal lobe epilepsy can cause sensory or emotional disturbances.
Ventricular system, formation,
Ventricular System and Formation of CSF
The ventricular system is a series of interconnected cavities (ventricles) within the brain that are filled with cerebrospinal fluid (CSF). This system supports and protects the brain by cushioning it, maintaining intracranial pressure, and facilitating the transport of nutrients and waste.
Components of the Ventricular System
Lateral Ventricles (First and Second Ventricles):
Located in each cerebral hemisphere.
Divided into regions: anterior horn, body, posterior horn, and inferior horn.
Connected to the third ventricle via the interventricular foramen (Foramen of Monro).
Third Ventricle:
A narrow, slit-like cavity located in the diencephalon between the two halves of the thalamus.
Connected to the fourth ventricle via the cerebral aqueduct (Aqueduct of Sylvius).
Fourth Ventricle:
Located between the cerebellum and the brainstem (pons and medulla).
Contains three openings:
Foramen of Magendie (median aperture).
Foramina of Luschka (two lateral apertures).
These openings allow CSF to flow into the subarachnoid space.
Central Canal:
A narrow canal extending from the fourth ventricle down through the spinal cord.
Formation of CSF
CSF is primarily produced in the choroid plexuses, specialized structures within the ventricles.
Steps in CSF Formation
Choroid Plexus Structure:
Located in the lateral, third, and fourth ventricles.
Comprised of:
Fenestrated capillaries: Allow plasma to filter out.
Ependymal cells: Line the capillaries and regulate CSF composition through active and passive transport.
Filtration and Secretion:
Blood plasma is filtered through the fenestrated capillaries.
Ependymal cells actively secrete ions (e.g., Na⁺, Cl⁻) into the ventricles, creating an osmotic gradient.
Water follows the osmotic gradient, forming CSF.
Composition of CSF:
Clear, colorless fluid with:
Low protein (15–45 mg/dL).
Glucose (~60% of plasma levels).
Ions (e.g., Na⁺, K⁺, Cl⁻, Mg²⁺).
~500 mL produced daily; total volume at any time is ~150 mL.
Circulation of CSF
Flow Pathway:
Lateral Ventricles → Interventricular Foramina (Foramina of Monro) → Third Ventricle → Cerebral Aqueduct → Fourth Ventricle → Subarachnoid Space via the Foramina of Magendie and Luschka.
Subarachnoid Space:
CSF circulates around the brain and spinal cord, providing cushioning.
Absorption:
CSF is reabsorbed into the venous blood through arachnoid granulations (villi) into the superior sagittal sinus.
Functions of the Ventricular System and CSF
Mechanical Protection:
Cushions the brain and spinal cord from mechanical trauma.
Buoyancy:
Reduces the effective weight of the brain, preventing compression of nerves and blood vessels.
Homeostasis:
Maintains a stable chemical environment for neuronal activity.
Waste Removal:
Removes metabolic waste products from the CNS.
Clinical Relevance
Hydrocephalus:
Excess CSF accumulation due to obstruction of flow, impaired absorption, or overproduction.
Types:
Communicating Hydrocephalus: Normal flow between ventricles but impaired absorption.
Non-communicating Hydrocephalus: Obstruction within the ventricular system (e.g., aqueductal stenosis).
CSF Leak:
Loss of CSF through trauma or surgery, causing low intracranial pressure and headaches.
Infections:
Meningitis: Inflammation of the meninges, often associated with altered CSF composition.
Circulation and Drainage of Cerebrospinal Fluid (CSF)
The circulation and drainage of CSF are essential for maintaining the brain’s homeostasis, cushioning the central nervous system (CNS), and facilitating the removal of waste products. The entire process involves the production of CSF in the ventricles, its circulation through the CNS, and its reabsorption into the bloodstream.
Circulation of CSF
Production:
CSF is produced primarily by the choroid plexuses located in the ventricles (lateral, third, and fourth ventricles).
Daily production: ~500 mL.
Total volume at any time: ~150 mL.
Flow Pathway:
Lateral Ventricles:
CSF is produced in the lateral ventricles, one in each cerebral hemisphere.
Interventricular Foramina (Foramina of Monro):
CSF flows from the lateral ventricles into the third ventricle.
Third Ventricle:
CSF continues through the third ventricle.
Cerebral Aqueduct (Aqueduct of Sylvius):
Connects the third ventricle to the fourth ventricle.
Fourth Ventricle:
CSF flows into the subarachnoid space through:
Median aperture (Foramen of Magendie).
Lateral apertures (Foramina of Luschka).
Subarachnoid Space:
CSF circulates around the brain and spinal cord within the subarachnoid space, providing cushioning and nutrient transport.
Drainage of CSF
Reabsorption:
CSF is reabsorbed into the bloodstream through arachnoid villi (projections of the arachnoid mater) and arachnoid granulations into the superior sagittal sinus.
The superior sagittal sinus is a large venous sinus located along the midline of the brain.
Venous Drainage:
From the superior sagittal sinus, CSF enters the venous system and drains into the internal jugular veins, eventually returning to the heart.
Mechanism of Reabsorption:
CSF reabsorption depends on a pressure gradient:
CSF pressure > Venous pressure: Allows CSF to flow into the venous system.