Nervous System and Central Nervous System: Study Guide for Anatomy & Physiology I

Chapter 11 – Nervous System and Nervous Tissue

Terminology of the Nervous System

The nervous system is a complex network responsible for communication, integration, and control throughout the body. Understanding key terms is essential for mastering this chapter.

• Neuron: The basic structural and functional unit of the nervous system.

• Glial cells: Supportive cells that assist neurons in function and maintenance.

• Synapse: The junction between two neurons or a neuron and an effector cell.

• Membrane potential: The voltage difference across a cell's plasma membrane.

Divisions of the Nervous System

The nervous system is divided into two main parts, each with distinct functions and structures.

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Composed of nerves and ganglia outside the CNS; transmits signals between the CNS and the rest of the body.

Division	Main Components	Function
CNS	Brain, Spinal Cord	Integration, Processing
PNS	Cranial & Spinal Nerves, Ganglia	Communication, Sensory & Motor Transmission

Glial Cells of the CNS and PNS

Glial cells provide structural and functional support to neurons. There are four types in the CNS and two in the PNS.

• CNS Glial Cells:

  • Astrocytes: Regulate the blood-brain barrier and provide nutrients.

  • Microglia: Act as immune cells, removing debris and pathogens.

  • Ependymal cells: Line ventricles and produce cerebrospinal fluid.

  • Oligodendrocytes: Form myelin sheaths around CNS axons.

• PNS Glial Cells:

  • Schwann cells: Form myelin sheaths around PNS axons.

  • Satellite cells: Surround neuron cell bodies in ganglia, regulate environment.

Structure and Function of a Neuron

Neurons are specialized for transmitting electrical signals. Their structure is closely related to their function.

• Cell Body (Soma): Contains the nucleus and organelles; metabolic center.

• Dendrites: Receive incoming signals from other neurons.

• Axon: Conducts electrical impulses away from the cell body.

• Myelination vs Non-myelination: Myelinated axons transmit signals faster due to insulation; non-myelinated axons transmit more slowly.

Example: In a typical motor neuron, dendrites receive signals, the cell body integrates them, and the axon transmits the response to muscles.

Functional Classification of Neurons

Neurons are classified based on their function:

• Sensory (Afferent) Neurons: Carry information from sensory receptors to the CNS.

• Motor (Efferent) Neurons: Transmit commands from the CNS to effectors (muscles/glands).

• Interneurons: Connect sensory and motor neurons within the CNS.

Membrane Potential

Membrane potential is the electrical charge difference across the neuron membrane, essential for signal transmission.

• Resting Membrane Potential: The stable voltage when a neuron is not transmitting signals; typically about $-70\ \text{mV}$.

• Graded Potential: Local changes in membrane potential; occur in dendrites and cell body, do not propagate far.

• Action Potential: Rapid, propagated change in membrane potential; occurs in axons, involves voltage-gated channels.

Key Steps in Action Potential:

1. Depolarization: Sodium channels open, $\text{Na}^+$ enters, membrane potential becomes less negative.

2. Repolarization: Potassium channels open, $\text{K}^+$ exits, membrane potential returns toward resting.

3. Restoration: Ionic balance restored by sodium-potassium pump.

Equation:

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

Example: Action potentials allow rapid communication along motor neurons to initiate muscle contraction.

Multiple Sclerosis

Multiple sclerosis is a disease characterized by the destruction of myelin sheaths in the CNS, leading to impaired signal transmission.

• Symptoms: Muscle weakness, vision problems, coordination difficulties.

• Pathology: Immune-mediated attack on oligodendrocytes.

Synapse

A synapse is the site of communication between neurons or between a neuron and an effector cell.

• Structure: Presynaptic terminal, synaptic cleft, postsynaptic membrane.

• Chemical Synapse Steps:

  1. Action potential arrives at presynaptic terminal.

  2. Voltage-gated calcium channels open.

  3. Calcium influx triggers neurotransmitter release.

  4. Neurotransmitter diffuses across synaptic cleft.

  5. Neurotransmitter binds to postsynaptic receptors.

  6. Postsynaptic response generated.

• Synaptic Delay: The brief time required for neurotransmitter release and binding.

Neurotransmitters

Neurotransmitters are chemical messengers released at synapses to transmit signals.

• Examples: Acetylcholine, dopamine, serotonin, glutamate.

• Functions: Excitatory or inhibitory effects on postsynaptic neurons; regulate mood, movement, cognition.

Chapter 12 – The Central Nervous System

Terminology of the Central Nervous System

The CNS is composed of the brain and spinal cord, responsible for integrating and processing information.

• Grey matter: Regions with neuron cell bodies.

• White matter: Regions with myelinated axons.

Four Regions of the Brain

The brain is divided into four main regions, each with specialized functions.

• Cerebrum

• Diencephalon

• Brainstem

• Cerebellum

Cerebrum

The cerebrum is the largest part of the brain, responsible for higher cognitive functions.

• Structures: Includes cerebral cortex, basal nuclei, and white matter tracts.

• Functions: Conscious thought, memory, voluntary movement.

• Five Lobes: Frontal, parietal, temporal, occipital, insula.

Lobe	Unique Functions	Overlapping Functions
Frontal	Motor control, decision-making	Speech (Broca's area)
Parietal	Sensory integration	Spatial awareness
Temporal	Auditory processing	Memory
Occipital	Visual processing	Visual association
Insula	Taste, visceral sensation	Emotion

Grey vs White Matter: Grey matter contains neuron cell bodies; white matter consists of myelinated axons.

Parkinson’s Disease & Huntington’s Disease: Both are neurodegenerative disorders affecting movement; Parkinson’s involves dopamine deficiency, Huntington’s involves genetic mutation.

Cerebral Cortex

The cerebral cortex is the outer layer of the cerebrum, responsible for conscious perception and voluntary actions.

• Four Generalizations:

  1. Each hemisphere controls the opposite side of the body.

  2. Hemispheres are not identical in function.

  3. Specific cortical areas have distinct functions.

  4. Functional areas are interconnected.

Functional Areas – Motor

Motor areas control voluntary movement.

• Primary Motor Cortex: Initiates voluntary movements.

• Motor Mapping: Somatotopic organization; different regions control different body parts.

• Premotor Cortex: Plans and coordinates complex movements.

• Broca’s Area: Controls speech production.

Functional Areas – Sensory

Sensory areas process incoming sensory information.

• Primary Sensory Cortex: Receives sensory input from the body.

• Somatosensory Association Cortex: Integrates sensory information for interpretation.

• Primary Visual Cortex: Processes visual information.

• Visual Association Area: Interprets visual data.

• Primary Auditory Cortex: Processes auditory signals.

• Auditory Association Area: Interprets sounds.

Example: The primary motor cortex sends signals to muscles for movement, while the primary sensory cortex receives touch information.