Nervous System and Special Senses: Exam 3 Study Guide

Nervous System Overview

Central vs. Peripheral Nervous System

The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Understanding their structure and function is essential for grasping how the body processes information and responds to stimuli.

• CNS: Consists of the brain and spinal cord; responsible for integrating, processing, and coordinating sensory data and motor commands.

• PNS: Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

• Key Difference: The CNS acts as the control center, while the PNS serves as the communication lines linking the body to the CNS.

• Example: Sensory input from the skin travels via the PNS to the CNS for processing.

Microscopic Structure of Nervous Tissue

Nervous tissue is composed of two main cell types: neurons and neuroglia.

• Neurons: Specialized for transmitting electrical impulses; consist of a cell body, dendrites, and an axon.

• Neuroglia: Support, protect, and nourish neurons; types include astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS, and Schwann cells and satellite cells in the PNS.

• Example: Oligodendrocytes form myelin sheaths in the CNS, increasing the speed of nerve impulse conduction.

Nerve Impulses and Synapses

Events in a Nerve Impulse

A nerve impulse, or action potential, involves a series of electrical events across the neuron's membrane.

• Resting Membrane Potential: The neuron is polarized, typically at -70 mV.

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

• Action Potential: If threshold is reached, a rapid change in membrane potential occurs.

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

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

Equation:

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

Electrical vs. Chemical Synapses

• Electrical Synapses: Direct passage of ions through gap junctions; rapid communication.

• Chemical Synapses: Neurotransmitters cross the synaptic cleft; slower but allows for modulation.

• Example: Most synapses in the CNS are chemical; electrical synapses are found in cardiac muscle.

Neurotransmitters

Neurotransmitters are chemicals that transmit signals across a synapse.

Class	Example	Function
Acetylcholine	Neuromuscular junctions	Excitatory or inhibitory
Amino acids	Glutamate, GABA	Main excitatory/inhibitory in CNS
Biogenic amines	Dopamine, serotonin	Mood, arousal, reward
Neuropeptides	Substance P, endorphins	Pain modulation

Brain and Spinal Cord Structure and Function

Brain Structure and Function

• Cerebrum: Higher brain functions (thought, memory, voluntary movement).

• Cerebellum: Coordination of movement and balance.

• Brainstem: Controls vital functions (breathing, heart rate).

Spinal Cord Structure and Function

• Gray Matter: Contains neuron cell bodies; site of synaptic integration.

• White Matter: Contains myelinated axons; transmits signals up and down the cord.

• Functions: Conducts sensory and motor information; mediates reflexes.

Spinal Cord Injuries

• Flaccid Paralysis: Damage to lower motor neurons; loss of muscle tone and reflexes.

• Spastic Paralysis: Damage to upper motor neurons; increased muscle tone, exaggerated reflexes.

Spina Bifida

• Definition: A neural tube defect resulting in incomplete closure of the spinal column.

• Homeostatic Imbalance: Can lead to paralysis, hydrocephalus, and other complications.

Autonomic Nervous System (ANS)

Somatic vs. Autonomic Nervous System

• Somatic: Voluntary control of skeletal muscles; single neuron pathway.

• Autonomic: Involuntary control of smooth muscle, cardiac muscle, and glands; two-neuron pathway (preganglionic and postganglionic).

• Neurotransmitters: Somatic uses acetylcholine; autonomic uses acetylcholine and norepinephrine.

Sympathetic vs. Parasympathetic Divisions

Division	Main Function	Neurotransmitter
Sympathetic	"Fight or flight"; increases heart rate, dilates pupils	Norepinephrine
Parasympathetic	"Rest and digest"; decreases heart rate, stimulates digestion	Acetylcholine

Autonomic Reflexes

• Autonomic Reflex Arc: Involves sensory input, integration in CNS, and motor output to effectors (e.g., heart, glands).

• Example: Baroreceptor reflex regulates blood pressure.

Homeostatic Imbalances

• Orthostatic Hypotension: Sudden drop in blood pressure upon standing; can be due to ANS dysfunction.

• Hypertension: Chronic high blood pressure; may involve overactive sympathetic division.

Special Senses

General vs. Special Senses

• General Senses: Touch, pain, temperature, proprioception; receptors distributed throughout the body.

• Special Senses: Vision, hearing, taste, smell, equilibrium; receptors located in specialized organs.

Special Sensory Receptors

• Photoreceptors: Detect light (retina of the eye).

• Mechanoreceptors: Detect sound and balance (ear).

• Chemoreceptors: Detect taste (tongue) and smell (olfactory epithelium).

Integration of Senses

• Sensory information is processed and interpreted by the CNS, allowing for perception and response to the environment.

• Special senses are integrated with other nervous system functions to maintain homeostasis and appropriate behavioral responses.

Homeostatic Imbalances of the Nervous System

• Disorders such as multiple sclerosis, spina bifida, and autonomic dysfunctions can disrupt normal nervous system function and homeostasis.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.