Organization of the Nervous System

1. Central Nervous System• The brain + the spinal cord

– The center of integration and control

2. Peripheral Nervous System• The nervous system outside

of the brain and spinal cord• Consists of:

– 31 Spinal nerves– 12 Cranial nerves

The Nervous System of a Vertebrate

• Central Nervous System (CNS)• contains fluid-filled spaces which contain cerebrospinal fluid (CSF).

–White matter is composed of bundles of myelinated axons

–Gray matter consists of unmyelinated axons, nuclei, and dendrites.

Figure 48.16x Spinal cord

Gray Matter

White Matter

Spinal Cord

Figure 48.20 The main parts of the human brain

• Cerebrum is the most highly evolved structure in the mammalian brain.

Functions: interpretation, initiating voluntary movements, storing memory, retrieving memory, reasoning, center for intelligence and personality

• Corpus Callosum is the major connection between the two hemispheres.

Corpus callosum

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

• Thalamus- leads to cerebral cortex, channeling impulses to appropriate part of cerebral cortex for interpretation

• Hypothalamus- Regulates autonomic activity involved in thermoregulation, hunger, thirst, sexual and mating behavior, etc… part of the limbic system (emotions)

• The pituitary gland is attached to the hypothalamus

Structure and Function• Brain stem--Consists of the medulla

oblongata, pons, and midbrain.

• Medulla Oblongata- Breathing, heart and blood vessel activity, swallowing, vomiting, digestion, and relays information to and from higher brain centers

• Pons- involved in the regulation of visceral activities such as breathing and relays info. to higher brain

Figure 48.28x1 Brain MRI

Mapping Language Areas of the Cerebral Cortex Max

Min

The Limbic System: Amygdala, Hippocampus, Olfactory Bulb

• Midbrain-integration of sensory information, in the regulation of visual and auditory reflexes, and relays as well

• Cerebellum error-checks and coordinates motor

activities, perceptual and cognitive factors. Relays sensory information about joints, muscles, sight, and sound to the cerebrum. Coordinates motor commands issued by the cerebrum; maintains posture

Peripheral Nervous System• Responsible for communication btwn the

CNS and the rest of the body.• Can be divided into:

–Sensory Division • Afferent division

–Conducts impulses from receptors to the CNS

–Motor Division • Efferent division

–Conducts impulses from CNS to effectors (muscles/glands)

Simple Nerve Path

The Knee-Jerk Reflex

Diversity in Nervous Systems

Overview of a Vertebrate Nervous System

Motor Efferent Division• Can be divided further:

–Somatic Nervous System• VOLUNTARY (generally)• Somatic nerve fibers that conduct impulses from the CNS to skeletal muscles

–Autonomic Nervous System• INVOLUNTARY (generally)• Conducts impulses from the CNS to smooth muscle, cardiac muscle, and glands.

Autonomic Nervous System

Parasympathetic and Sympathetic Nervous Systems

Structure of a Vertebrate Neuron

Neuron Shape is Dependent on Numbers of Synapses

Axon

Neurons

Types of Neurons• Sensory Neurons afferent; carry impulses to

CNS• Interneurons link neurons in the CNS• Motor Neurons carry impulses away from CNS

to effectors such as muscles and glands• SUPPORT CELLS Of Nervous System• Schwann Cells: peripheral nervous system—

produce myelin sheath• Oligodendrocytes: CNS; myelinating cell• Astrocytes: CNS; form scar tissue, mop up

excess ions, etc, induce synapse formation, connect neurons to blood vessels

Synaptic Transmission• An AP reaches the

axon terminal and causes V-gated Ca2+ channels to open.

• Ca2+ rushes in & initiates NT exocytosis.

• NTs diffuse across the synaptic cleft and then bind to receptors on the postsynaptic membrane and initiate some sort of response on the postsynaptic cell.

Schwann Cells

A Chemical Synapse

Nerve Impulses:http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter44/the_nerve_impulse.html

Transmission Across a Synapse:http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter44/transmission_across_a_synapse.html

Synaptic Transmission:

http://www.pol2e.com/at34.03.html

Neurons and Synapses:http://www.pol2e.com/at34.04.html

The Major Known Neurotransmitters

Put Some Ach Into It! http://www.pol2e.com/mc34.01.html

Forces Behind Resting PotentialSelective Permeability- some molecules

pass through membrane more freely than others; ion channels

Sodium-Potassium Pump- transports 3 Na out of, 2 K into cell

Result:Concentration GradientElectrical Gradient

The Basis of the Membrane Potential

Resting Membrane Potential:http://bcs.whfreeman.com/thelifewire/content/chp44/4402001.html

Resting Potential:http://www.biologyalive.com/life/classes/apbiology/documents/Unit%204/48_Lectures_PPT/media/48_10RestingPotential_A.swf

The Sodium-Potassium Pump: a Specific Case of Active Transport

Sodium-Potassium Exchange Pump:http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/sodium-potassium_exchange_pump.html

Resting Potential: http://www.biologyalive.com/life/classes/apbiology/documents/Unit%204/48_Lectures_PPT/media/48_10RestingPotential_A.swf

Resting Membrane Potential:http://bcs.whfreeman.com/thelifewire/content/chp44/4402001.html

Voltage-Gated Channels and the Action Potential:http://highered.mcgraw-hill.com/olc/dl/120107/anim0013.swf

Molecular Basis of Action Potential – transmission of

a signal along an axon

Sodium channels open once threshold is reached, influx of sodium

Potassium channels open at AP peak; potassium flows out

Generating an Impulse• polarized membrane: inside is negative relative to

the outside under resting conditions due to distribution of ions controlled by Na+/K+ pump that require ATP

• Nerve impulse starts when the membrane of the nerve depolarizes due to some stimulus, chemical, temp. changes, mechanical, etc….

• Depolarization is caused by the influx of Na+ which causes the membrane to become more positive. This starts an action potential, or nerve impulse. They follow the all or none law!!!

• The membrane will repolarize when K+ leaves the cell setting the membrane back to resting potential or polarized

• This de and repolarization continues down the nerve until it reaches another nerve to pass on the impulse or until it reaches an effector.

Propagation of the Action Potential

The Action Potential

http://www.pol2e.com/at34.02.html

http://www.biologyalive.com/life/classes/apbiology/documents/Unit%204/48_Lectures_PPT/media/48_13ActionPotential_A.swf

Saltatory Conduction

Graded potentials and the action potential in a neuron

What are the two components of the Central Nervous System?

What are the two components of the Peripheral Nervous System?

The two hemispheres of the brain are connected by the:

Last Review Questions for the Week:

What are the two components of the Peripheral Nervous System?

What type of response is processeddirectly in the spinal cord with no impulses traveling to the brain?

Which part of the neuron receives impulses? carries them away?

Describe what occurs at the axon terminal to cause the transmission of a nerve impulse from one neuron to the next.

What is the minimum level of a stimulus required to cause an actionpotential in a neuron called?

What is meant by the term, “all-or-none principle” with regards to the conduction of nerve impulses?

What is the difference between a reflex and a normal response?

Draw two neurons side by side and label the cell bodies, myelin sheaths, axon terminals, synapse, nodes, and place of neurotransmitter secretion.

Describe what happens during an action potential including movement of the appropriate ions across the axon and the correct charges inside and outside the cell.

Describe the path of a nerve impulse that would occur when someoneyou don’t like touches your hand and you pull your hand away. Use the following terms:motor neurons, hand, interneurons, sensory neurons, effector (muscle), brain, spinal cord.