Central and Peripheral Nervous System: Study Guide for ANP College Students

Central Nervous System: The Spinal Cord

Basic Structures and Functions of the Spinal Cord

The spinal cord is a major component of the central nervous system, serving as a conduit for information between the brain and the rest of the body. It is responsible for transmitting sensory and motor signals and mediating reflexes.

• Structure: Cylindrical, extends from the foramen magnum to the lumbar region.

• Function: Conducts nerve impulses, coordinates reflexes, and integrates incoming and outgoing information.

• Example: Withdrawal reflex when touching a hot object.

Spinal Meninges and Spaces

The spinal cord is protected by three connective tissue layers called meninges, which surround and cushion it.

• Dura mater: Outermost, tough layer.

• Arachnoid mater: Middle, web-like layer.

• Pia mater: Innermost, delicate layer adhering to the cord.

• Spaces: Epidural (outside dura), subdural (between dura and arachnoid), subarachnoid (between arachnoid and pia, contains cerebrospinal fluid).

Organization of Spinal Cord White Matter

White matter in the spinal cord is organized into columns (funiculi) that contain ascending (sensory) and descending (motor) tracts.

• Ascending tracts: Carry sensory information to the brain.

• Descending tracts: Carry motor commands from the brain to the body.

• Patterns: Tracts are grouped by function and direction.

Main Sensory Tracts and Motor Pathways

Sensory and motor pathways are essential for communication between the body and the central nervous system.

• Sensory tracts: Dorsal column, spinothalamic, spinocerebellar.

• Motor pathways: Corticospinal, rubrospinal, vestibulospinal.

• Roles: Sensory tracts transmit touch, pain, and proprioception; motor pathways control voluntary and involuntary movements.

Organization of Spinal Cord Grey Matter

Grey matter is organized into horns, each with distinct functions and neuron types.

• Dorsal (posterior) horn: Contains sensory neurons.

• Lateral horn: Contains autonomic motor neurons (present in thoracic and upper lumbar regions).

• Ventral (anterior) horn: Contains somatic motor neurons.

Dorsal Root, Dorsal Root Ganglion, and Ventral Root

These structures are critical for the transmission of sensory and motor information.

• Dorsal root: Carries sensory information into the spinal cord.

• Dorsal root ganglion: Contains cell bodies of sensory neurons.

• Ventral root: Carries motor information out of the spinal cord.

Peripheral Nervous System

Definition and Components

The peripheral nervous system (PNS) consists of all nerves and ganglia outside the central nervous system. It connects the CNS to limbs and organs.

• Components: Cranial nerves, spinal nerves, ganglia, and plexuses.

General Structure of a Nerve

Nerves are bundles of axons surrounded by connective tissue layers.

• Structure: Axons (nerve fibers), endoneurium, perineurium, epineurium.

Structure of a Spinal Nerve and Distribution of Rami

Spinal nerves emerge from the spinal cord and branch into rami that serve different regions.

• Dorsal ramus: Serves the back.

• Ventral ramus: Serves the limbs and anterior trunk.

• Communicating ramus: Connects to autonomic ganglia.

Types of Neurons in Mixed Nerves

Mixed nerves contain both sensory and motor neurons.

• Sensory neurons: Transmit information to the CNS.

• Motor neurons: Transmit commands from the CNS to muscles and glands.

Ganglion

A ganglion is a collection of neuron cell bodies in the PNS.

• Function: Relay and integrate information.

Plexus

A plexus is a network of intersecting nerves. Major plexuses include:

• Cervical plexus: Serves neck and diaphragm.

• Brachial plexus: Serves upper limb.

• Lumbar plexus: Serves lower limb.

• Sacral plexus: Serves lower limb and pelvic region.

Distribution and function: Each plexus gives rise to peripheral nerves that innervate specific regions.

Reflex Arc Components and Types of Reflexes

A reflex arc is the neural pathway for reflex actions. Reflexes can be autonomic (involuntary) or somatic (voluntary).

• Components: Receptor, sensory neuron, integration center, motor neuron, effector.

• Autonomic reflexes: Affect internal organs.

• Somatic reflexes: Affect skeletal muscles.

Types of Reflexes

Reflexes are classified by their function and response.

• Stretch reflex: Maintains muscle tone (e.g., knee-jerk).

• Flexor reflex: Withdrawal from painful stimulus.

• Crossed-extensor reflex: Balances body during withdrawal.

• Tendon reflex: Prevents muscle damage from excessive force.

Events Leading to Sensation and Perception

Sensation and perception involve the detection and interpretation of stimuli.

• Sensation: Activation of sensory receptors.

• Perception: Interpretation of sensory input by the brain.

• Steps: Stimulus, receptor activation, impulse transmission, CNS processing.

Cranial Nerves

There are twelve pairs of cranial nerves, each with a specific function. They are identified by name and Roman numeral.

Number	Name	Main Function	Type
I	Olfactory	Smell	Sensory
II	Optic	Vision	Sensory
III	Oculomotor	Eye movement	Motor
IV	Trochlear	Eye movement	Motor
V	Trigeminal	Facial sensation, chewing	Mixed
VI	Abducens	Eye movement	Motor
VII	Facial	Facial expression, taste	Mixed
VIII	Vestibulocochlear	Hearing, balance	Sensory
IX	Glossopharyngeal	Taste, swallowing	Mixed
X	Vagus	Viscera control	Mixed
XI	Accessory	Neck muscles	Motor
XII	Hypoglossal	Tongue movement	Motor