Unit #7 Nervous System:

Neurons

Maintaining homeostasis• Two systems of communication–Nervous system

• Rapid response• Uses action potentials

–Endocrine system• Slower response• Uses hormones released into blood stream

• Controlled by the NS

Did You Know?

• Many types of mental illnesses are related to imbalances in chemicals that transmit messages between neurons

Central nervous system: Brain and spinal cordPeripheral nervous system: all nervous tissue outside the CNS- nerves going to organs and muscles

Organization of the nervous system

• I. Somatic (SNS): sensory neurons send information into to brain via somatic receptors

• II Autonomic (ANS) sends messages from internal organs to brain. Sends messages to smooth and cardiac muscles & glands from the brain. Under involuntary control

• III. Enteric (ENS) the “brain of the gut” controls digestion, peristalsis, secretions of GI tract organs. Involuntary control

Divisions of the PNSTortora Fig 9.1 pg 254

Master glands- hypothalamus and pituitary- located in brain– Communicate with other e. organs by hormones

Regulates growth, development, metabolism, and homeostasis in the body

Endocrine system

Functions of the nervous system

I. Sensory function-Detect and transmit information to the brain • Sight• Hearing• Touch• Taste• Smell

II. Integrative• The NS processes sensory information– Analysis– Storage (memory)

– Decisions– Responses

Functions of Nervous System

III. MotorOnce info. is integrated, a motor response is generated by activating effectors(muscles and glands).Stimulation causes muscles to contract and glands to secrete.

Functions of Nervous System

3 distinct areas

• Cell body (soma)

• Dendrites• Axons• Messages travel from the dendrites towards the axon

Neurons: cells of the nervous system

– Nucleus– Typical cell organelles

– No mitotic spindle.

– Will the cell divide?

Neuron organelles

.

– Usually short and thick.

– Usually highly branched.

– Receives impulses.

– Conducts impulses towards cell body.

Dendrites

Dendrites surrounded by neuroglial cells.

• Axons– Neurons have a single axon.

– Usually long and very thin.

– Can be branched (collaterals)

– Axon terminals contain vesicles.

– Vesicles contain neurotransmitters.

Axons

Axon surrounded by neuroglial

cells

Tortora256

–Multipolar–Bipolar–Unipolar

3 types of

neurons:

• Multipolar: have several dendrites, 1 axon- brain, spinal cord neurons

• Bipolar: 1 main dendrite, 1 axon- retina of eye, inner ear, olfactory area of brain

• Unipolar: dendrites & axon are fused together, cell bodies off to the side (in ganglia)- sensory receptors (touch, pain, thermal)

Functional classification

• Sensory, Motor, and Connecting Neurons– Sensory are referred to as afferent.

– Motor are referred to as efferent.

– Connecting are referred to as association

• Somatic Vs Autonomic– Somatic is voluntary• Sensory nerves and motor nerves.

– Autonomic is involuntary• Mostly motor nerves leading to smooth muscle, cardiac muscle, and glands.

Organization of Nervous System

Neurons and neuroglia• Two different types of cells– Neurons conduct impulses.

– Neuroglial cells support and protect neurons.

Neurons found in the spinal cord.

• Neuroglia cells– Smaller than neurons.

– Outnumber neurons 5 to 50 times.

– Function: support, protect neurons

make cerebrospinal fluid, create the myelin sheathGlioma: brain tumor made of glial cells : malignant

• Myelin sheath– Speeds impulse along axon.

– Insulates axon .

– Composed of neuroglial cells. (PNS)

– Schwann cells produce myelin (lipoprotein) in PNS

– Nodes of Ranvier are gaps in myelin sheath.

Myelin sheath

Myelin sheath structure

White and gray

matter– White matter is myelinated: axon is surrounded by a myelin sheath

– Gray matter is unmyelinated- axon (not wrapped)

Nerve Impulses

• Nerve impulse– An impulse is a change in the electrical charge (potential) on the membrane of the neuron.

– Due to ions moving into and out of the neuron.

Nerve Impulses

– Ions move through very selective membrane channels.

– Channels are transmembrane proteins.

– Voltage gated channels pass pulse down the axon to the terminus

Tortora

Pages 260-262

• Membrane Potentials– Resting potential - no impulse.• Positive outside• Negative inside.

– Action potential.• Positive inside.• Negative outside.

– Potentials are due to ions.• Na +

• K+

• Large negative ions (proteins)

Nerve Impulses

Tortora

Pages 261

Nerve Impulses

• Resting potential– No impulse.– Positive outside neurolemma

– Negative inside.– 30x more K+ inside.– 15x ore Na+ outside.– Large negative ioins trapped inside.

– Sodium - Potassium pump creates these conditions.

– Membrane is “polarized”.

Tortora

Pages 210-213

Creating An Impulse Along An Axon

Continuous and saltatory conduction

Caffeine & the Nervous System

Conduction Across

Synapses• Impulses are sent to:– Glands– Muscles– Other neurons.

• Impulse must bridge the synapse for the message to be sent

Conduction Across Synapses• Synapses have ability to transmit impulses or inhibit impulse transmission.

Na+/K+

PumpVoltage gated

channelsConduction

Across A Synapse

Conduction Across

Synapses• Presynaptic neuron– Synaptic vesicles

– Neurotransmitter

– Role of calcium ions

• Synaptic cleft

• Postsynaptic neuron.– receptors

Synaptic disruptions• Most brain disorders involve disruption of synaptic communication.

• Toxins can block both the transmission and reception of neurotransmitters.

What is a nerve?

• Nerves are groups of neurons.– Mixed contain dendrites and axons.

– Motor contain axons only. (Efferent)

– Sensory contain dendrites only. (Afferent)

REGENERATION OF NERVOUS TISSUE• Neurons have limited powers of regeneration.

• Neurons ability to reproduce is lost at 6 months of age.

• A destroyed neuron is lost.

• PNS neurons can repair.

• CNS neurons cannot repair.

Axon regeneration