Study Guide: Nervous System and Neural Physiology (Chapters 11, 12, 13)

Objectives and Study Preparation

This study guide outlines the key objectives and topics you are required to master for the exam covering Chapters 11, 12, and 13 of Anatomy & Physiology. The focus is on the nervous system, including neural and nervous tissue physiology, the central and peripheral nervous systems, and spinal cord anatomy and function.

• Resources for Preparation:

  • Lecture slides and personal notes

  • Group study/quizzing

  • Textbook chapters and practice tests

• Exam Format:

  • Multiple choice, short answer, and case study questions

  • Coverage of all major topics from the specified chapters

Neural/Nervous Tissue and Neural/Nervous Physiology (Chapter 11)

Neurotransmitters and Neuron Anatomy

Neurons communicate via chemical messengers called neurotransmitters. Understanding their function and the structure of neurons is essential for grasping nervous system physiology.

• Neurotransmitters: Chemicals that transmit signals across a synapse from one neuron to another. Examples include acetylcholine, dopamine, and serotonin.

• Neuron Anatomy: Key structures include the cell body (soma), dendrites, axon, axon terminals, and myelin sheath.

• Hyperpolarization: Occurs when the membrane potential becomes more negative than the resting potential, making neurons less likely to fire.

• Depolarization: Occurs when the membrane potential becomes less negative (more positive), increasing the likelihood of neuron firing.

• Resting Membrane Potential: The electrical potential difference across the membrane of a resting neuron, typically around $-70\,\text{mV}$.

• Action Potential: A rapid change in membrane potential that travels along the axon, allowing neurons to communicate.

Example: When a neuron receives a stimulus, sodium channels open, causing depolarization. If the threshold is reached, an action potential is generated and propagated along the axon.

Synaptic Transmission and Integration

Neurons communicate at synapses, where neurotransmitters are released to transmit signals to other neurons or effector cells.

• Synapse: The junction between two neurons, consisting of the presynaptic terminal, synaptic cleft, and postsynaptic membrane.

• Excitatory Postsynaptic Potential (EPSP): Depolarizes the postsynaptic membrane, increasing the likelihood of an action potential.

• Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes the postsynaptic membrane, decreasing the likelihood of an action potential.

• Summation: The process by which multiple EPSPs and IPSPs combine to determine whether a neuron will fire.

Example: If enough EPSPs are generated at the axon hillock, the neuron will reach threshold and fire an action potential.

Membrane Channels and Potentials

Neurons possess various membrane channels that regulate ion flow and membrane potential.

• Types of Channels: Voltage-gated, ligand-gated, and mechanically-gated channels.

• Graded Potentials: Local changes in membrane potential that vary in size and decay over distance.

• Action Potentials: All-or-none electrical impulses that propagate without decrement.

Equation:

$V_m = V_{inside} - V_{outside}$

Where $V_m$ is the membrane potential.

The Central Nervous System (CNS) and Peripheral Nervous System (PNS) (Chapters 12 & 13)

Brain Structure and Function

The brain is the central organ of the nervous system, protected by the skull and meninges. It is divided into several regions, each with specialized functions.

• Major Brain Regions: Cerebrum, cerebellum, diencephalon (thalamus, hypothalamus), and brainstem (midbrain, pons, medulla oblongata).

• Protection: The brain is protected by the skull, meninges (dura mater, arachnoid mater, pia mater), and cerebrospinal fluid (CSF).

• White Matter vs. Gray Matter: White matter consists of myelinated axons; gray matter contains neuron cell bodies and dendrites.

• Primary Motor Cortex: Controls voluntary movements; located in the precentral gyrus of the frontal lobe.

• Primary Sensory Cortex: Processes sensory information; located in the postcentral gyrus of the parietal lobe.

Example: Damage to the primary motor cortex can result in loss of voluntary movement on the opposite side of the body.

Cranial Nerves

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

Cranial Nerve	Function
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	Visceral sensation, parasympathetic control (mixed)
XI. Accessory	Neck muscles (motor)
XII. Hypoglossal	Tongue movement (motor)

Additional info: Cranial nerves are numbered I-XII from anterior to posterior.

Peripheral Nervous System (PNS)

The PNS consists of nerves and ganglia outside the CNS, including cranial and spinal nerves.

• Spinal Nerves: 31 pairs, each arising from the spinal cord and serving specific body regions.

• Plexuses: Networks of nerves (cervical, brachial, lumbar, sacral) that innervate limbs and trunk.

• Mixed Nerves: Contain both sensory and motor fibers.

Example: The brachial plexus supplies nerves to the upper limb.

Spinal Cord Anatomy and Function (Chapter 13)

Spinal Cord Structure

The spinal cord is a cylindrical structure that transmits neural signals between the brain and the body.

• Gray Matter: Contains neuron cell bodies; forms the central "H" shape in cross-section.

• White Matter: Contains myelinated axons; surrounds the gray matter.

• Ascending Tracts: Carry sensory information to the brain.

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

• Spinal Nerves: Emerge from the spinal cord; each has dorsal (sensory) and ventral (motor) roots.

Example: Damage to the descending tracts can result in motor deficits below the level of injury.

Spinal Reflexes

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

• Types of Reflexes: Stretch reflex (e.g., knee-jerk), withdrawal reflex, crossed extensor reflex.

• Components: Sensory receptor, sensory neuron, integration center, motor neuron, effector.

Example: The patellar reflex is a monosynaptic stretch reflex that helps maintain posture.

Spinal Nerve Plexuses

Plexus	Major Nerves	Region Served
Cervical	Phrenic nerve	Neck, diaphragm
Brachial	Axillary, radial, median, ulnar nerves	Shoulder, arm, hand
Lumbar	Femoral nerve	Anterior thigh
Sacral	Sciatic nerve	Posterior thigh, leg, foot

Additional info: Some nerves from different plexuses may combine to form major peripheral nerves.

Summary Table: Key Nervous System Structures

Structure	Function
Neuron	Transmit electrical impulses
Synapse	Site of neurotransmitter release
CNS	Integration and processing of information
PNS	Relay information to and from CNS
Spinal Cord	Conduit for signals; reflex center
Cranial Nerves	Sensory and motor functions of head/neck
Spinal Nerves	Sensory and motor functions of trunk/limbs

Additional info: These study notes expand upon the provided objectives and questions, offering definitions, examples, and tables for comprehensive exam preparation on the nervous system chapters.