Study Guide: The Spinal Cord, Brain, Cranial Nerves, and Autonomic Nervous System

Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes

Spinal Meninges and Spaces

The spinal cord is protected by three layers of connective tissue called meninges, which surround the cord and associated spaces.

• Dura mater: Outermost, tough layer.

• Arachnoid mater: Middle, web-like layer.

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

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

• Spinal Regions: Four spinal cord regions/levels:

• Cervical: Upper part of the spine (spinal nerves C1 through C8)

• Thoracic: Upper middle part of the spine (Spinal nerves T1 through T12)

• Lumbar:Lower Middle part of the spine (Spinal nerves L1 through L5)

• Sacral: Lower part of the spine (Spinal nerves S1 through S5, Co1)

Example: Epidural anesthesia is administered into the epidural space.

Spinal Cord Anatomy

The spinal cord consists of four main regions: cervical, thoracic, lumbar, and sacral.

• Surface anatomy: Enlargements (cervical and lumbar) correspond to limb innervation.

• Gray matter: Central, butterfly-shaped region containing neuron cell bodies.

• White matter: Surrounds gray matter, contains myelinated axons organized into tracts.

Example: The cervical enlargement supplies nerves to the upper limbs.

Spinal Nerves and Pathways

Spinal nerves connect the spinal cord to the body, transmitting sensory and motor information.

• Somatic vs. visceral pathways: Somatic pathways control voluntary muscles; visceral pathways regulate internal organs.

• Motor and sensory roots: Dorsal roots carry sensory information; ventral roots carry motor signals.

Example: The dorsal root ganglion contains sensory neuron cell bodies.

Spinal Reflexes

Reflexes are rapid, involuntary responses to stimuli, mediated by the spinal cord.

• Monosynaptic reflex: Involves a single synapse (e.g., patellar reflex).

• Polysynaptic reflex: Involves multiple synapses (e.g., withdrawal reflex).

• Stretch reflex: Maintains muscle tone and posture.

• Tendon reflex: Prevents muscle damage from excessive tension.

Example: The patellar reflex is a classic monosynaptic stretch reflex.

Ascending and Descending Tracts

Tracts are bundles of axons in the white matter that carry information up and down the spinal cord.

• Ascending tracts: Carry sensory information to the brain.

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

Example: The spinothalamic tract transmits pain and temperature sensations.

Chapter 14: The Brain and Cranial Nerves

Cranial Meninges and Spaces

The brain is protected by cranial meninges, similar to those of the spinal cord, and associated spaces.

• Major folds: Falx cerebri, tentorium cerebelli, falx cerebelli.

• Major fluid-filled spaces: Ventricles, subarachnoid space.

Example: The falx cerebri separates the two cerebral hemispheres.

Ventricular System and Cerebrospinal Fluid (CSF)

The ventricular system consists of interconnected cavities filled with CSF, which cushions and nourishes the brain.

• Production: CSF is produced by the choroid plexus.

• Flow: CSF circulates through ventricles and subarachnoid space.

Example: Hydrocephalus results from impaired CSF flow.

Major Brain Regions and Functions

The brain is divided into several major regions, each with distinct functions.

• Cerebrum: Higher cognitive functions, sensory processing, voluntary movement.

• Diencephalon: Thalamus (sensory relay), hypothalamus (homeostasis).

• Brainstem: Midbrain, pons, medulla oblongata (vital functions, cranial nerves).

• Cerebellum: Coordination and balance.

Example: The medulla oblongata controls heart rate and respiration.

Cranial Nerves

There are 12 pairs of cranial nerves, each with specific sensory, motor, or mixed functions.

• Olfactory (I): Smell

• Optic (II): Vision

• Oculomotor (III): Eye movement

• ... (others up to XII)

Example: The facial nerve (VII) controls facial expression and taste.

Functional Areas and Cortical Organization

The cerebral cortex contains specialized areas for sensory, motor, and association functions.

• Primary motor cortex: Voluntary movement

• Primary sensory cortex: Sensory perception

• Association areas: Integration and interpretation

Example: Broca's area is involved in speech production.

Chapter 16: The Autonomic Nervous System and Higher-Order Functions

Autonomic Nervous System (ANS) Organization

The ANS regulates involuntary functions via sympathetic and parasympathetic divisions.

• Sympathetic division: Prepares body for 'fight or flight' responses.

• Parasympathetic division: Promotes 'rest and digest' activities.

• Autonomic ganglia: Relay stations for ANS signals.

Example: Sympathetic activation increases heart rate.

Neurotransmitters and Effects

ANS uses specific neurotransmitters to communicate with target organs.

• Acetylcholine (ACh): Used by both divisions at preganglionic synapses; parasympathetic postganglionic synapses.

• Norepinephrine (NE): Used by sympathetic postganglionic synapses.

Example: NE causes vasoconstriction in blood vessels.

Visceral Reflexes and Higher-Order Functions

Visceral reflexes control internal organ function; higher-order functions include memory, sleep, and consciousness.

• Short vs. long reflexes: Short reflexes bypass CNS; long reflexes involve CNS integration.

• Memory: Includes short-term, long-term, and consolidation processes.

• Sleep: Stages include REM and non-REM; regulated by reticular activating system.

• Dementia: Progressive decline in cognitive function; causes include Alzheimer's disease.

Example: The reticular activating system maintains consciousness.

Key Terms and Definitions

Term	Definition
Arachnoid villi	Projections of the arachnoid mater into the dural sinuses, allowing CSF reabsorption.
Autonomic ganglia	Clusters of neuronal cell bodies in the ANS where preganglionic neurons synapse with postganglionic neurons.
Cauda equina	Bundle of spinal nerve roots at the lower end of the spinal cord.
Celiac ganglion	Major autonomic ganglion in the abdomen, part of the sympathetic nervous system.
Central pattern generator	Neural circuits that produce rhythmic outputs for activities like walking.
Cranium	The skull, which encases and protects the brain.
Denticulate ligament	Extensions of pia mater that anchor the spinal cord to the dura mater.
Fenestrated capillary	Capillaries with pores that allow for increased permeability.
Fornix	Arching fiber tract in the brain connecting hippocampus to other regions.
Intramural ganglion	Ganglia located within the walls of target organs (parasympathetic division).
Lissencephaly	Developmental disorder resulting in a smooth brain surface due to lack of gyri.
N-methyl-D-aspartate (NMDA) receptor	Glutamate receptor involved in synaptic plasticity and memory.
Postural reflex	Reflexes that maintain posture and balance.
Septum pellucidum	Thin membrane separating lateral ventricles in the brain.
Shingles	Viral infection of spinal nerves causing painful rash.
Spinal nucleus	Cluster of neuron cell bodies within the spinal cord.
Subdural hemorrhage	Bleeding between dura mater and arachnoid mater.
Sympathetic chain	Series of interconnected sympathetic ganglia alongside the vertebral column.
Tract	Bundle of axons in the CNS with a common origin and destination.
Varicosity	Swelling along an axon where neurotransmitters are released in the ANS.