Bio Bases

THE NERVOUS SYSTEM

The nervous system receives and transmits information.

A. Central nervous system (CNS): consists of the brain and spinal cord. The brain is split into right and left

hemispheres, which exhibit contralateral control (each hemisphere controls opposite side of body) and

lateralization (left and right hemispheres have different functions). The three major parts of the brain are the

hindbrain, midbrain, and forebrain.

1. Hindbrain: the top part of the spinal cord; includes the medulla, pons, and cerebellum

a. Medulla: controls basic biological functions, such as breathing, swallowing, and balance

b. Pons: controls facial expressions, sleep, and dreaming

c. Cerebellum: controls fine motor movements

2. Midbrain: coordinates basic movements with sensory information

3. Forebrain: large in humans; includes the cerebral cortex and subcortical structures such as the thalamus,

hypothalamus, and basal ganglia

a. Basal ganglia: regulates muscle contractions/movements

b. Thalamus: incorporates and relays sensory information to the cortex

c. Hypothalamus: controls motivated behavior, such as eating, drinking, and sex

d. Hippocampus: helps process and receive long-term and spatial memory

e. Amygdala: controls emotion and evaluation of stimuli

f. Cerebral cortex: receives sensory information and transmits motor information. The corpus callosum is a

nerve tract beneath the cortex that connects the two hemispheres and allows them to communicate. The

cerebral cortex consists of four lobes:

• Occipital lobe: processes vision

• Temporal lobe: processes sound

• Parietal lobe: integrates sensory systems; is involved in attention

• Frontal lobe: controls speech, learning, thinking, decision-making, and abstract thought

B. Peripheral nervous system: includes all nerves that spread through the body from the brain and spinal cord. The

peripheral nervous system has two divisions:

1. Somatic division: controls voluntary muscle movements and sense organs

2. Automatic division: controls involuntary actions and the internal organs; divided into two parts:

a. Sympathetic nervous system: gets the body ready for emergency action

b. Parasympathetic nervous system: becomes active during states of relaxation

II. NEURONS

Neurons, or nerve cells, are the basic unit of the nervous system. Each neuron has three main parts.

A. Soma: cell body; stores energy for the cell

B. Dendrite: receives messages from other neurons and conducts the messages toward the soma

C. Axon: sends messages to other neurons

1. Terminal branches (axon terminals): the end of the axon that contains neurotransmitters

2. Myelin sheath: insulates axons so signals can travel quickly

a. Glial cell: creates myelin, supports and guides neurons, and helps repair neurons

III. INFORMATION EXCHANGE

Neurons communicate by receiving and transmitting nerve impulses.

A. The axon terminals of the presynaptic neuron are stimulated. The terminals contain synaptic vesicles, which empty

neurotransmitters into the synapse between the neurons. Neurotransmitters activate the postsynaptic neuron,

changing its voltage. Once the excitation threshold is reached, the action potential begins, and a neuron fires.

1. Synapse: the small gap between neurons where information is exchanged

2. Synaptic vesicles: places where neurotransmitters are stored until release into the synapse

3. Neurotransmitters: chemicals that stimulate neurons so they can communicate

a. Excitatory: make neurons more likely to fire

b. Inhibitory: make neurons less likely to fire

4. Excitation threshold: the voltage difference (-55 millivolts) necessary to destabilize a neuron, causing an action

potential to occur

5. Action potential (nerve impulse): the brief change in electrical charge that destabilizes a neuron. The action

potential stimulates the axon terminals, restarting the process.

IV. ENDOCRINE SYSTEM

The endocrine system, made up of hormone-secreting glands, affects communication inside the body.

A. Hormones are chemicals that help regulate bodily functions

B. Glands produce hormones and dump them into the blood-stream, through which hormones travel through the body.

C. Hormones act more slowly than neurotransmitters, but their effects tend to be longer-lasting.