The Nervous System

Neurons: specialized cells of the nervous system.

3 major regions:– 1) Dendrites: receive

signals from other neurons

– 2) Cell Body: contains the nucleus and organelles

– 3) Axon: Carries impulse signal to other neurons/muscles

– 4) Myelin sheeth – surrounds portions of the axon to protect and insulate.

Types of neurons:

Sensory: Send impulses from receptors in the sense organs to the spinal cord and brain.

Motor: Carry a signal from brain and spinal cord to glands/muscles.

Interneuron: Found in the spinal cord and brain. Sends messages between sensory and motor neurons.

Reflex arc

A reflex is an preprogrammed response to a certain stimulus.

In a reflex a sensory neuron sends a message to the spinal cord which immediately relays a response to a motor neuron.

The brain does not interpret the response until after it has happened!

Nerve Impulse – charge traveling through a neuron.

1. A stimulus is received by a sensory neuron.

2. The impulse is sent towards the spinal cord and then up to the brain to receive the message.

3. The brain sends a response to a motor neuron with reaction instructions.

Action-Potential Nerves: All or nothing!

In order for nerves to send an impulse, they rely upon the concentration of ions to function properly. Specifically Sodium and Potassium ions control impulses.

At rest: Slightly negative inside the cell, slightly positive outside.

Stimulus causes pumps to activate, dumping positive sodium ions outside the cell and pulling in less potassium – reversing the charges on either side of the membrane.

Sodium-Potassium Pumps

To allow for action potentials, a protein pump is used.

The one protein dumps 3 positive charges out of the cell (Na+) and pulls in 2 K+ ions.

Each time the pump makes this switch, ATP is used.

Impulses

The impulse travels the length of the nerve cell’s axon until it reaches the end.

Between 2 neurons there is a gap called a synapse.

The impulse causes the axon to send neurotransmitters to the dendrites of the next neuron to continue the message.

Organization of the Nervous System: 2 Divisions

The nervous system has 2 divisions: Central Nervous System (CNS)

– Brain and spinal cord– Mostly interneurons

Peripheral Nervous System (PNS)– Sensory and motor neurons that carry info to and

from CNS.

CNS - Brain

Cerebrum: Largest portion. – Involved with learning, memory,

speech/language, senses and voluntary movement.

Cerebellum: Found in the back.– Controls balance and coordination,

smooth muscle (involuntary movement).

Medulla Oblongata: Relays signals between brain and spinal cord.

– Controls breathing rate, heart rate, and blood pressure.

CNS – Spinal Cord

Extends from the brain to the lower back

Protected by the spinal column or vertebrae.

Reflexes are processed by the spinal cord.

PNS -

Subdivided into Somatic and Autonomic.

Somatic Nervous System relay info from sensors to CNS.

– comprises voluntary actions

Autonomic carries impulses from CNS to heart and other internal organs.

– Comprise involuntary actions (out of your control).

Autonomic Divisions

Sympathetic and Parasympathetic divisions.– Sympathetic Nervous System act in times of

stress: High heart rate and breathing.– Parasympathetic Nervous System active when

the body is relaxed.

– Both relay messages to the same organs, but the over responses depends on which division is in control.

Drug Effects

A drug is a substance that alters some function of the body. Certain drugs:

– change the amount of neurotransmitters released.– Block receptors of neurotransmitters.– Imitate neurotransmitters.

Types of drugs:– Stimulants: Increase activity

Caffine Nicotine

– Depressants: Decrease CNS, blood pressure and heart rate. Often raise levels of dopamine creating a happy feelings.

Alcohol Inhalants Illegal drugs

Disorders

Meningitis – and inflammation of the meninges.

This can be life threatening and lead to a number of other disorders if not treated.

Multiple Sclerosis – Breakdown of the myelin protective coverings around neurons.

Can cause paralysis, loss of function, cognitive issues and death if untreated.