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

Organization of the nervous system Central nervous system: Brain and spinal cord Peripheral nervous system: all nervous tissue outside the CNS- nerves going to organs and muscles

Tortora Fig 9.1 pg 254 Divisions of the PNS 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

Endocrine system Master glands- hypothalamus and pituitary- located in brain Communicate with other e. organs by hormones Regulates growth, development, metabolism, and homeostasis in the body

Functions of the nervous system I. Sensory function-Detect and transmit information to the brain Sight Hearing Touch Taste Smell

Functions of Nervous System II. Integrative The NS processes sensory information Analysis Storage (memory) Decisions Responses

Functions of Nervous System III. Motor Once info. is integrated, a motor response is generated by activating effectors (muscles and glands). Stimulation causes muscles to contract and glands to secrete.

Neurons: cells of the nervous system 3 distinct areas Cell body (soma) Dendrites Axons Messages travel from the dendrites towards the axon

Neuron organelles Nucleus Typical cell organelles No mitotic spindle. Will the cell divide? .

Dendrites surrounded by neuroglial cells. Usually short and thick. Usually highly branched. Receives impulses. Conducts impulses towards cell body. Dendrites surrounded by neuroglial cells.

Axon surrounded by neuroglial cells Tortora 256 Axons Neurons have a single axon. Usually long and very thin. Can be branched (collaterals) Axon terminals contain vesicles. Vesicles contain neurotransmitters. Axon surrounded by neuroglial cells

3 types of neurons: Multipolar Bipolar Unipolar

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

Organization of Nervous System 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.

Neurons found in the spinal cord. 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 sheath Glioma: brain tumor made of glial cells : malignant

Myelin sheath structure 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 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. Tortora Pages 260-262 Ions move through very selective membrane channels. Channels are transmembrane proteins. Voltage gated channels pass pulse down the axon to the terminus

Nerve Impulses Membrane Potentials Resting potential - no impulse. Tortora Pages 261 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)

Creating An Impulse Along An Axon Nerve Impulses Tortora Pages 210-213 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”. 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.

Conduction Across Synapses Presynaptic neuron Synaptic vesicles Neurotransmitter Role of calcium ions Synaptic cleft Postsynaptic neuron. receptors Voltage gated channels Na+/K+ Pump Conduction Across A Synapse

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