The Human BodyThe Nervous System

Textbook Chapter 14

Review Book Topic 1

Neuron Structure

• Specialized cells that help you gather information about your environment, interpret the information, and react to it

• Make up the communication network of your body known as the nervous system

• Three major parts– Dendrites

• Receive signals (impulses) from other neurons• Conducts impulses to cell body• Single neuron has many dendrites

– Cell body• Contains nucleus and other cell organelles

– Axon• Carries nerve impulse from cell body to other

neurons and muscles

• Types of neurons– Sensory neurons

• Send impulses from receptors in skin and sense organs to the brain and spinal cord

• Signal interneurons

– Interneurons• Found in spinal cord and brain• Carry impulse to motor neurons

– Motor neurons• Carries impulses away from brain and spinal cord

to a gland or muscle• Results in a response

• Reflex Arc– Nerve pathway that consists of a

sensory neuron, an interneuron, and a motor neuron

– Reflex ~ quick response to a change in the environment

– Brain is NOT involved (doesn’t require conscious thought)

– Involuntary

– Basic structure of the nervous system

Nerve Impulse

• Nerve impulse is an electrical charge traveling the length of a neuron

• Impulses result from a stimulus

• A neuron at rest is not conducting an impulse

• A stimulus causes nerve impulse, opening channels within the cell membrane, moving charge particles (ions) across the membrane (creating a concentration gradient)

• Charge is passed along the length of the axon

– Can be slow or fast

– Axons can be covered with a myelin sheath (lipid) which insulate the nodes of the axon

• With myelin ~ carry impulses associated with sharp pain (faster)

• Without myelin ~ carry impulses associated with dull, throbbing pain (slower)

– How quickly the charge goes from node to node determines the reaction time

• A small gap exists between the axon of one neuron and the dendrites of another

– Known as a synapse

– Vesicles move the chemical signal across this gap to continue the pathway of the impulse

• Neurotransmitter– Chemical that diffuses across a synapse and

binds to receptors on the dendrite of a neighboring neuron

– 25 known types

– Can be broken down by enzymes or recycled

Neuron BrainPop

Organization of the Nervous System

• Two divisions– Central nervous system (CNS)

• Brain and spinal cord

– Peripheral nervous system (PNS)• Sensory and motor neurons• Carries information to and

from CNS

• Mostly interneurons

• Coordinates all of the body’s activities

• Relays messages, processes information, and analyzes responses

Central Nervous System

• Sensory neurons carry information about the environment to the spinal cord

• Interneurons in the spinal cord might respond via a reflex arc or they might relay information to the brain

– Brain sends messages by way of spinal cord to motor neurons and body responds or brain stores information to be recalled later

• Brain

– 100 billion neurons found here

– Maintains homeostasis

– Involved with almost all of the body’s activities

– Control center of the body

• Parts– Cerebrum

• Largest part of the brain

• Divided into two halves called hemispheres

–Not independent of each other–Connected to each other by a

bundle of nerves

• Carries out thought processes involved with learning, memory, language, speech, voluntary body movement, and sensory perception

• Higher thought processes occur near the surface of the brain

• Folds and grooves on the surface increase the surface area and allows for more complicated processes

– Cerebellum• Controls balance, posture and coordination• Located in the back of the brain• Controls smooth and coordinated movement of

skeletal muscles • Involved with motor skills

– Brain stem connects the brain to the spinal cord and is made of two regions• Medulla oblongata

–Relays signals between the brain and spinal cord

–Helps control breathing rate, heart rate, and blood pressure

–Contains interneurons that form a reflex arc for swallowing, vomiting, coughing, and sneezing

• Pons–Relays signals between the cerebrum

and cerebellum

–Helps control the rate of breathing

– Hypothalamus• Located between brain stem and cerebrum

• Essential for maintaining homeostasis

• Regulates body temperature, thirst, appetite, and water balance

• Partially regulates blood pressure, sleep, aggression, fear, and sexual behavior

• Size of a fingernail

• Performs more function that any other brain structure of its size

• Spinal cord– Nerve column that extends

from the brain to the lower back

– Protected by vertebrate

– Spinal nerves extend from spinal cord to parts of the body and connect them to the CNS

– Reflexes are processed here

• Nerves are made up of bundles of axons made from sensory and motor neurons

• 12 Cranial nerve that lead to and from the brain

• 31 spinal nerves (and their branches) that lead to and from the spinal cord

Peripheral Nervous System

• Two classifications– Somatic nervous system– Autonomic nervous system

• Somatic nervous system– Nerves relay information from external sensory

receptors to the CNS

– Motor neurons relay information from CNS to skeletal muscles

– Voluntary

– Reflexes mostly go to the spinal cord and not to the brain

• Autonomic nervous system– Carries impulses from the CNS to the heart

and other internal organs

– Involuntary

– Not under conscious control

– “Fight-or-flight” response or

“rests-and-digests”

Nervous System

Central Nervous System

Peripheral nervous System

Somatic Nervous System

(voluntary)

Relays info to and from skin and

skeletal muscles

Autonomic Nervous System

(involuntary)

Relays info to internal organs

Nervous System BrainPop