Nervous System and Special Senses: Comprehensive Study Guide

Nervous System Overview

Basic Functions of the Nervous System

The nervous system is responsible for controlling and coordinating body activities. It enables communication between different body parts and the environment.

• Sensory Input: Gathering information from sensory receptors about internal and external changes.

• Integration: Processing and interpreting sensory input to determine an appropriate response.

• Motor Output: Activation of effector organs (muscles and glands) to cause a response.

Divisions of the Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integration and command.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

• Somatic Nervous System: Controls voluntary movements via skeletal muscles.

• Autonomic Nervous System (ANS): Regulates involuntary functions (e.g., heart rate, digestion); subdivided into sympathetic and parasympathetic divisions.

Neural Tissue and Cells

Types of Neural Cells

• Neurons: Excitable cells that transmit electrical signals.

• Neuroglia (Glial Cells): Support, protect, and nourish neurons. Types include astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS; Schwann cells and satellite cells in the PNS.

Neuron Structure

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

• Dendrites: Receive incoming signals.

• Axon: Conducts impulses away from the cell body.

• Myelin Sheath: Insulating layer that increases the speed of impulse transmission.

Neurophysiology

Resting Membrane Potential

The resting membrane potential is the voltage difference across the neuron's plasma membrane when the cell is at rest, typically around -70 mV.

• Maintained by the sodium-potassium pump and differential permeability of the membrane to ions.

Action Potentials

• Depolarization: Na+ channels open, Na+ enters the cell, making the inside more positive.

• Repolarization: K+ channels open, K+ leaves the cell, restoring negative charge inside.

• Hyperpolarization: Membrane potential becomes more negative than resting potential.

Equation:

$V_m = V_{in} - V_{out}$

Synaptic Transmission

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

• Neurotransmitters: Chemical messengers (e.g., acetylcholine, norepinephrine) released from synaptic vesicles to transmit signals across the synaptic cleft.

Central Nervous System (CNS)

Brain Regions and Functions

• Cerebrum: Responsible for higher brain functions, including thought, memory, and voluntary movement.

• Diencephalon: Includes thalamus (sensory relay) and hypothalamus (homeostasis, endocrine control).

• Brainstem: Includes midbrain, pons, and medulla oblongata; controls vital functions such as breathing and heart rate.

• Cerebellum: Coordinates movement and balance.

Spinal Cord

• Conducts sensory and motor information between the brain and the body.

• Contains ascending (sensory) and descending (motor) tracts.

Protective Structures

• Meninges: Three connective tissue membranes (dura mater, arachnoid mater, pia mater) that protect the CNS.

• Cerebrospinal Fluid (CSF): Cushions the brain and spinal cord, provides nutrients, and removes waste.

Peripheral Nervous System (PNS)

Nerve Structure and Function

• Cranial Nerves: 12 pairs, primarily serve the head and neck.

• Spinal Nerves: 31 pairs, connect the CNS to the rest of the body.

• Reflex Arcs: Simple neural pathways that mediate reflex actions.

Somatic vs. Autonomic Nervous System

Feature	Somatic	Autonomic
Control	Voluntary	Involuntary
Effector Organs	Skeletal muscles	Cardiac muscle, smooth muscle, glands
Neurotransmitter	Acetylcholine	Acetylcholine, norepinephrine

Autonomic Nervous System (ANS)

Divisions of the ANS

• Sympathetic Division: Prepares the body for 'fight or flight' responses; increases heart rate, dilates pupils, inhibits digestion.

• Parasympathetic Division: Promotes 'rest and digest' activities; decreases heart rate, stimulates digestion.

Neurotransmitters in the ANS

• Acetylcholine: Released by all preganglionic neurons and most parasympathetic postganglionic neurons.

• Norepinephrine: Released by most sympathetic postganglionic neurons.

Special Senses

Olfactory System (Smell)

• Olfactory Receptors: Located in the nasal cavity; detect odorants.

• Olfactory Bulb: Processes olfactory information and relays it to the brain.

Gustatory System (Taste)

• Taste Buds: Sensory organs for taste, located on the tongue and other oral surfaces.

• Primary Tastes: Sweet, sour, salty, bitter, umami.

Visual System (Sight)

• Photoreceptors: Rods (dim light, black and white vision) and cones (color vision, bright light) in the retina.

• Optic Nerve: Transmits visual information from the retina to the brain.

Auditory System (Hearing)

• Outer Ear: Collects sound waves.

• Middle Ear: Transmits vibrations via ossicles (malleus, incus, stapes).

• Inner Ear: Contains cochlea (hearing) and vestibular apparatus (balance).

Equilibrium (Balance)

• Vestibular Apparatus: Semicircular canals and otolith organs detect head position and movement.

Clinical Considerations

Common Disorders

• Stroke: Disruption of blood flow to the brain, causing tissue damage.

• Multiple Sclerosis: Demyelination of CNS neurons, leading to impaired function.

• Parkinson's Disease: Degeneration of dopamine-producing neurons in the substantia nigra.

• Alzheimer's Disease: Progressive neurodegenerative disorder affecting memory and cognition.

Reflex Testing

• Patellar Reflex: Knee-jerk response; tests integrity of the spinal cord and peripheral nerves.

• Babinski Reflex: Abnormal in adults; indicates CNS damage if present.

Summary Table: Major Brain Regions and Functions

Region	Main Functions
Cerebrum	Conscious thought, memory, voluntary movement
Diencephalon	Sensory relay, homeostasis, endocrine control
Brainstem	Vital functions (breathing, heart rate), reflexes
Cerebellum	Coordination, balance

Key Terms and Definitions

• Ganglion: Cluster of neuron cell bodies in the PNS.

• Nucleus (CNS): Cluster of neuron cell bodies in the CNS.

• Tract: Bundle of axons in the CNS.

• Nerve: Bundle of axons in the PNS.

• Dermatome: Area of skin supplied by a single spinal nerve.

• Plexus: Network of intersecting nerves.

Additional info:

• Some explanations and context have been expanded for clarity and completeness based on standard Anatomy & Physiology curricula.

• Tables and definitions have been inferred and organized for exam preparation purposes.