The Nervous System
• Controls and coordinates the body’s responses to changes in the environment
• HOW:• Stimulus ≡ a change in the
external or internal environment which initiates an impulse
• Impulse ≡ an electro-chemical charge generated along a neuron
The Nervous System
• Receptors ≡ structures specialized to detect certain stimuli
• Response ≡ a reaction to a stimulus
• Effectors ≡ what responds to a stimulus such as muscles or glands
Neurons• Neuron ≡ Basic Unit of the Nervous System
• Neurons conduct impulses throughout the nervous system.
• A neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon.
• Dendrites ≡ receive impulses and carry them toward the cell body
• Axon ≡ carries impulses away from the cell body and toward other neurons, muscles, or glands.
• Cell body ≡ contains the nucleus
Neurons
2003-2004
signaldirection
myelin coating
Myelin sheath coating Axon coated with insulation
made of myelin cells speeds signal
signal hops from node to node
330 mph vs. 11 mph
Multiple Sclerosis immune system (T cells) attacks myelin coating loss and/or slowing of signal impulse
Multiple Sclerosis immune system (T cells) attacks myelin coating loss and/or slowing of signal impulse
2003-2004
Facts about neurons• Most specialized cell in
animals• Longest cell
– blue whale neuron• 10-30 meters
– giraffe axon• 5 meters
– human neuron• 1-2 meters
Nervous system allows for 1 millisecond response timeNervous system allows for 1 millisecond response time
Types of Neurons
3 Types of neurons• 1. Sensory neurons: carry impulses from the body
to the spinal cord and brain (sense receptors)• 2. Motor neurons carry the response impulses
away from the brain and spinal cord to a muscle or gland. (effectors)
• 3.Interneurons: connect sensory &motor neurons within the brain and spinal cord
2003-2004
Types of neuronssensory neuron(from senses)
interneuron(brain & spinal chord)
motor neuron(to muscle)
How an impulse is transmitted• 1. Resting: no impulse, cell is polarized ( + on outside & - on
inside)– Sodium/Potassium pump in axon using ATP maintains this
polarity (active transport);slower
How an impulse is transmitted• 2.Impulse: stimulus excites
neuron– Na+ channels open– Na+ goes inside, therefore
inside becomes more +– Depolarization occurs = a
nerve impulse– Impulse moves in one
direction– Depolarization works with
concentration gradient
2003-2004
Synapse: a connection
synapse
• Junction between nerve cells• Connection between neurons &
effector cells
2003-2004
Synapse: a connection
synapse
– 1st cell releases chemical (neurotransmitter) to trigger next cell
– where drugs affect nervous system
2003-2004
The Nervous Systems
• Central nervous system (CNS)– brain & spinal cord
• Peripheral nervous system (PNS)– nerves from senses– nerves to muscles/glands– Both systems work together
cerebrum
cerebellum
spinal cord cervicalnerves
thoracicnerves
lumbarnerves
femoral nerve
sciatic nerve
tibialnerve
Anatomy of the brain• Cerebrum:
– Conscious activities– Intelligence– Memory– Language– Voluntary activity
• Cerebellum:A̶ Coordinates motor activity & balance
Anatomy of the brain• Midbrain:
A̶ reptilian brain (instincts, emotions)
• Hindbrain/Brain stem:A̶ Medulla Oblongata: involuntary activities such as breathing & heart rate
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Somatic Nervous
System (voluntary)
Relays information to and from skin and skeletal
muscles.
Nervous System
Autonomic Nervous
System (involuntary)
Relays information to internal organs.
Sympathetic Nervous
System Controls organs in times of stress.
Parasympathetic Nervous System
Controls organs when body is at rest
The Nervous System