The Nervous System

Anatomy & Physiology 2

Organization of the nervous System

• Central nervous system (CNS) – the brain and spinal cord

– Interprets incoming sensory information and issues instructions based on past experiences and current conditions

• Peripheral nervous system (PNS) – the nerves that extend from the brain and spinal cord

– Link and carry all the information to the CNS

Organization of the nervous System

• The PNS is divided into 2 subdivisions– Sensory division:

keeps the CNS informed of events going on both inside and outside the body

– Motor division: activates muscles and glands

Organization of the nervous System

• The motor division has two subdivisions:– Somatic nervous

system: voluntary controls the body

– Autonomic nervous system: regulates involuntary activities

Nervous Tissue

• Nerve Cells– The main part of the nervous

system

– The human body contains numerous nerve cells

– Nerve cells are called neurons

– Neurons are similar to electrical wires and carry messages along long, thin strands

– They can reach up to a meter in length

– A nerve is a bunch of neurons bunched together

Nervous Tissue

• Nerve Cells– Have all the organelles that

other cells have, but look very different

– Dendrites receive information from other neurons

– Axons sends information to other neurons

– A synapse is a connection between 2 neurons

Nervous Tissue

• Nerve fibers are covered with a whitish, fatty material called myelin

• When the myelin completely cover the nerve cells it called the myelin sheath

• It’s function is to make nerve cells faster

Nervous Tissue

• Not all cells are mylinated

• In the brain there are dense collections of myelinated regions called white matter and dense collections of unmyelinated regions called gray matter

Pathway of Messages

• Information is sent on 2 different pathways – it is not the same pathway

• For example: if you touch something hot the information is sent to your brain on one pathway and the result of touching something hot (it burns) is sent on another pathway

• Nerve cells do not touch one another – the information skips across the synapse

Nervous System Parts

• • Nerve cells are important parts of the nervous system, but others include:

• The brain– The organ that sends, receives

and processes information from all body parts

– It is made of billons of neurons

• Spinal cord– Carries information from the

brain to the body– All information from the body

is first sent to the spinal cord, then to the brain

The Brain

The Brain

• Parts:– Cerebrum

– Diencephalon (interbrain)

– Brain stem

– Cerebellum

The Brain

• Cerebrum– The cerebrum has two

cerebral hemispheres

– Has elevated ridges of tissue called gyri and shallow grooves called sulci which provide landmarks

– Controls thought, reason, senses, speech, memory, consciousness, interpretation of sensation and voluntary movement

The Brain

• Cerebrum– Occipital lobe – visual area

– Temporal lobe – auditory area

– primary motor area – controls movement

– Broca’s area – involved in speech

– Frontal lobe – intellectual reasoning and socially acceptable behavior

The Brain

• Cerebrum– Corpus callosum –

connects the cerebral hemispheres

• Diencephalon– Sits atop the brain stem

– Contains the thalamus, hypothalamus and epithalamus

The Brain

• Diencephalon– Thalamus: quickly

recognizes pleasant or unpleasant sensations

– Hypothalamus: controls body temp, water balance and metabolism; also drives emotions

– Epithalamus: important to the endocrine system

The Brain

• Brain stem– About the size of a human

thumb

– 3 parts midbrain, pons, medulla oblongata

– Midbrain: controls and directs incoming impulses

– Pons: helps control breathing

– Medulla oblongata: controls heart rate, blood pressue, breathing, swallowing and digestion

The Brain

• Cerebellum– Has two hemispheres

– Large cauliflower-like structure under the occipital lobe

– Helps make movement smooth and not robot-like and controls balance

Nervous System Parts

• Spinal Cord– About 17 inches long – Can be thought of as the power

lines from the power plant– Spinal cord is protected by

vertebrae (series of bones)

• Is a two-way passage system• All the nerves that extend from

the spinal cord are called body nerves

Reflexes

• Reflexes are reactions that are quick and protective

• During a reflex the message does not reach the brain first, but reacts, then tells the brain the information

• How a reflex works– If you put your hand on a hot

stove the information is sent to your spinal cord through one pathway, through another pathway information is sent back to your hand to move, along yet another pathway information is sent to your brain and finally through another pathway information is sent to your hand that it hurts