Nervous SystemsChapter 48

Recognizes and coordinates the body’s response to changes in its internal and external environments. ◦ Sensory input – vision, hearing, balance, smell,

taste, and touch ◦ Motor output – muscle contraction and movement ◦ Memory and integration of information

General Functions

All animals except sponges have a nervous system

What distinguishes nervous systems of different animal groups is how neurons are organized into circuits

A Circuit of Neurons

Specialized cells that carry electrical signals called impulses

3 Types of Neurons: ◦ Sensory – carry impulses from the sense organs

to the spinal cord and brain ◦ Motor – carry impulses from brain and spinal cord

to muscles and glands ◦ Interneurons – Connect sensory and motor

neurons and carry impulses between them

The Neuron

Automatic responses to stimuli Controlled by 5-part reflex arc:

◦ 1. Sensory receptor reacts to stimulus (heat on finger)

◦ 2. Impulse is carried to the spinal cord by a sensory neuron

◦ 3. In the spinal cord, the impulse is transferred to a motor neuron

◦ 4. Motor neuron conducts a nerve impulse to an effector (arm muscles)

◦ 5. Effector responds to the impulses by contracting (hand gets pulled away from the heat)

Reflexes: Different Types of Neurons Working Together

Cnidarians, sea stars◦ Nerve nets

Flatworms, leeches◦ Relatively simple

cephalization, have a central nervous system (CNS)

Annelids, arthropods◦ Ganglia (arranged clusters

of neurons) connect to CNS, making a peripheral nervous system (PNS)

Organization of Nervous Systems

At rest, the outside of the cell has a net positive charge, and the inside has a net negative charge. ◦ This charge difference is called

the resting potential (-70mVolts).

This charge difference is due to active transport by the sodium-potassium pump.

The sodium-potassium pump moves sodium (Na+) outside the cell, and potassium (K+) inside the cell.

The Resting Neuron

1. An impulse begins when a neuron is stimulated by another neuron or by the environment.

2. Sodium pores open on the membrane and sodium ions diffuse into the neuron.

3. The internal charge goes from -70 mVolts to +30 mVolts.

4. This is called the action potential.

The Nerve Impulse Begins

5. The influx of sodium stimulates the opening of potassium pores and (K+) flows out.

6. This restores the resting potential to normal.

7. But now all of the sodium is inside and the potassium is outside.

How does the cell go back to its original condition? ◦ The sodium/potassium pump

kicks in. 8. The depolarization on one

segment starts a domino effect down the neuron.

The gap between the axon of one neuron and the dendrites or cell body of the next neuron.

When the impulse reaches the end of the axon, chemicals called neurotransmitters are released and carry the impulse to the next neuron.

The Synapse

Organization of the Vertebrate Nervous System

Cerebrum ◦ Largest region; folds and

grooves increase surface area

◦ Controls voluntary activities and all higher brain functions (intelligence, learning and judgment)

◦ Right and left hemispheres are connected by corpus callosum

CNS: The Brain

Cerebellum ◦ Center for balance and

coordination of voluntary muscle movements.

Brain Stem ◦ Relays information between brain

and spinal cord ◦ Comprised of the pons and

medulla oblongata ◦ Work together to control

involuntary processes like breathing, heart rate, blood pressure, digestion, and swallowing

Thalamus ◦ Relay station for all sensory

input to the cerebrum.

Hypothalamus ◦ Homeostatic center that

controls endocrine system (hormones), body temperature, thirst, hunger, fatigue, etc.

Two main functions: ◦ Reflex center ◦ Carries info to and from brain to body

CNS: The Spinal Cord

Receives information from the environment and relays to and from CNS and sensory, motor and gland cells

Two divisions: Sensory and Motor Motor is divided into:

◦ Somatic NS (voluntary) responds to external stimuli. 1.Regulates activities that are under conscious control (e.g.

picking your nose) 2.Some reflex control

◦ Autonomic (involuntary) NS respond to internal stimuli; two divisions: Sympathetic ↑energy consumption (increase HR) Parasympathetic ↓energy consumption (decrease HR) Both help maintain homeostasis by having opposing effects

Peripheral Nervous System

Autonomic Nervous System

Bell’s Palsy – unexplained episode of facial weakness or paralysis

Dementia - damaged brain cells caused by injury or disease (Alzheimer’s); memory loss, confusion and personality change

Migraine Headaches – caused by a drop in serotonin levels? (triggered by stress, hormones, certain foods)

Multiple sclerosis (MS) – myelin sheaths deteriorate resulting in progressive loss of coordination

Parkinson’s – uncontrollable shaking caused by damage to dopamine transmitters; no cure

Tay-Sachs – fatal genetic lipid storage disorder where fat builds up on brain tissues and neurons during the first few months of life causing mental and physical deterioration

Nervous System Disorders

Stimulants Accelerate HR, BP, and breathing rate Increases the release of neurotransmitters;

leads to release of energy and feeling of well-being

When effect wears off, brain’s supply is depleted leaving the user depressed and fatigued ◦ Caffeine – prevents binding of adenosine ◦ Cocaine – sudden release of dopamine ◦ Methamphetamines – same effect as cocaine

Drugs and the Nervous System

Depressants Slow down HR, lower BP and breathing rate,

relax muscles and relieves anxiety ◦ Alcohol – physical and mental impairment,

depression, liver damage ◦ Marijuana – more lung damage than cigarettes;

memory loss, reduced levels of testosterone in males

◦ Sleeping Pills

Drugs and the Nervous System