Chapter 29 The brain

Central Nervous System

It is the complex of nerve tissues that controls the activities of the body. In vertebrates, it is comprised of the brain, spinal cord, and optic nerves. It controls thoughts processes, guides movement, and registers sensations.

Peripheral Nervous System

It consists of all the nerves outside of the brain and spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. It is divided into the somatic nervous system and autonomic nervous system.

Somatic Nervous System

The part of the peripheral nervous system that is under voluntary control, and transmits signals from the brain to end organs such as muscles. It consists of sensory neurons, and motor neurons.

Autonomic Nervous System

The autonomic nervous system controls involuntary responses to regulate physiological functions. The most notable physiological effects from autonomic activity are pupil constriction and dilation, and salivation of saliva. The autonomic nervous system is always activated, but is either in the sympathetic or parasympathetic state.

Parasympathetic Nervous System

The part of the involuntary nervous system that serves to slow the heart rate, increase intestinal and glandular activity, and relax the sphincter muscles. It allows the body to function in a "rest and digest" state.

Sympathetic Nervous System

It is activated during a “fight or flight” situation in which great mental stress or physical danger is encountered. Neurotransmitters such as norepinephrine, and epinephrine are released, which increases heart rate and blood flow in certain areas like muscle, while simultaneously decreasing activities of non-critical functions for survival, like digestion.

Sensory Neurons

Nerve cells within the nervous system responsible for converting external stimuli from the organism's environment into internal electrical impulses. They carry messages from receptors in the body to the CNS.


A neuron that transmits impulses between different neurons.

Motor Neurons

Neurons that carry messages from the CNS back to the muscles and glands in response to an impulse.

Neuromuscular Junction

It is a synapse between a neuron and a muscle. There are 5 steps of a signal transmission at a neuromuscular junction. Action potentials travel along the neuron’s axon to the axon terminals. Arrival of the action potential at an axon terminal triggers the release of neurotransmitters into the synaptic cleft. Motor neurons release the neurotransmitter acetylcholine (ACh). ACh binds to receptors on skeletal muscles, allowing Na+ to pass into these cells. Subsequent action potentials stimulate muscle contraction


Neurotransmitter that is released during muscle contractions.

Norepinephrine and Epinephrine

Neurotransmitters that are released during stress response of excitement.


It is a region where axon terminals transmit neurotransmitters to another cell

White Matter

Consists of myelinated axons. It connects various gray matter areas of the brain to each other and it carries nerve impulses between neurons.

Gray Matter

Consists of axon terminals, cell bodies, dendrites, and neuroglial cells. It is where all the synapses are.

Cerebral Cortex

The outer gray matter layer of the cerebrum which is responsible for most complex behavior. Like making reasoned choices, concentrating on tasks, planning for the future, behaving appropriately in social situations. They are four lobes of the brain which are the temporal lobe, the occipital lobe, the parietal lobe, and the frontal lobe. The frontal lobe deals with thinking, behavior, memory, and movement. The parietal lobe deals with language and touch. The occipital lobe deals with sight. The temporal lobe deals with hearing, learning, and feelings.

Limbic System

It is a group of structures that are located deep in the brain, and it functions in expression of emotion

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