THE NERVOUS SYSTEM Divisions of the NS Central

THE NERVOUS SYSTEM

Divisions of the NS • Central Nervous System (CNS) • Peripheral Nervous System (PNS) Fig. 11. 32

Sensory vs. Motor Nerves • SENSORY nerves: – Body CNS • MOTOR nerves: Fig. 10. 2 – CNS Body

2 Different Types of Motor Nerves • Somatic NS – consciously controlled effectors • Autonomic NS – involuntary effectors

Cells of the Nervous System • NEURONS vs. • NEUROGLIAL CELLS

NEUROGLIAL CELLS • • Fill spaces Provide structure Produce myelin Phagocytize bacteria & cellular debris • Outnumber neurons • Can divide (mitosis)

Neuron Anatomy Overview • Dendrites Cell body Axon Synaptic knobs at axon terminals Effector

Neuron Anatomy • Schwann cells – type of neuroglial cell – myelin sheath • Nodes of Ranvier Fig. 10. 3

Classification of Neurons THE DIRECTION THEIR SHAPE Fig. 10. 6

Sensory, Motor, and Interneurons (Direction) • Sensory neurons – PNS CNS • Motor neurons – CNS PNS • Interneurons – in between sensory and motor neurons Fig. 10. 7

Shapes of Neurons Fig. 10. 6

Neuron vs. a “Nerve” Fig. 11. 24 • Neuron = a cell • Nerve = bundles of neuron axons, and neuroglial cells bound together – outside brain/spinal cord

Neuron Physiology • Sending neuron impulses = action potential – change in electrical charge in cell membrane – depends on electrolytes • potassium (K+) and sodium (Na+)

First Things First: Creating a Resting Potential • Protein pumps – open and close – let ions through • Active pumps – against a gradient Fig. 10. 13 Na+/K+ Pump • Passive pumps – with the gradient

Resting Potential Fig. 10. 14

Action Potential Fig. 10. 15 Action Potential

A Nerve Impulse- a series of action potentials Fig. 10. 16 Computer activity http: //outreach. mcb. harvard. edu/animations/actionpotential. swf

Action Potential Fig. 10. 18 Action Potential Zoomed Out

What happens when the nerve impulse reaches the end of the axon? • axon terminals – next to another neuron (as shown) or a muscle or gland • Gap called a synapse Synapse Fig. 10. 11

The Synapse • • Neurotransmitters Synaptic cleft Receptors Send a message Fig. 10. 12

Neurotransmitters

Classification of Neurotransmitters • EXCITATORY = depolarize the next neuron • It tells the next neuron/muscle/gland to GO • INHIBITORY = hyperpolarize the next neuron – prevent the nerve impulse from continuing • It tells the next neuron/muscle/gland to STOP

Acetylcholine (ACH) • First neurotransmitter discovered (1921) • Mostly excitatory • Skeletal muscle neuromuscular junctions & synapses between the brain and spinal cord • Message = – muscles contract or – continue sending impulses

Acetylcholine cont. • Nicotine – Activates acetylcholine receptors – Releases dopamine (coming later…) • Alzheimers – Memory loss, depression, disorientation, dementia, hallucinations, death – Deficient acetylcholine

Glutamate • Generally excitatory – helps send messages in the brain • Involved in learning and memory • Alcohol inhibits glutamate receptor function • Monosodium Glutamate (MSG) – food additive – stimulates glutamate receptors in the taste buds

Serotonin • Found in the brain • Primarily inhibitory • Sleep, mood and temperature regulation • Insomnia – deficient serotonin • Antidepressants (Prozac, Zoloft, Paxil, etc) – “SSRI’s” or Selective Serotonin Reuptake Inhibitors – Serotonin accumulates in the synapse – feel more content • LSD blocks serotonin • MDMA releases excess serotonin

Dopamine • AKA “the brain reward” • Regulates emotions, moods and subconscious control of skeletal muscle • Nicotine – excess dopamine release • Cocaine – blocks reuptake (leaves more in the synapse) • Methamphetamine – excess dopamine release

Dopamine - cont’d • Dopamine also sends signals that help coordinate your skeletal muscle movements • Parkinson’s Disease – deficient dopamine production – tremors

GABA • Found in the brain • Generally inhibitory • Prevents the receptor nerve from being overstimulated • When it accumulates it has a sedative effect • Valium, Xanax and Ativan work by allowing GABA to accumulate • Huntington’s Disease – deficient GABA

Norepinephrine • Found in the brain • Alertness, regulation of moods • Ritalin & Adderallincrease level of norepi and dopamine • Strattera- increase only norepi • Clinical depression – low norepi

Endorphins • Flood the synaptic cleft during pain or stress – Usually inhibit neurons from firing, causing an analgesic effect – At lower levels can excite the next neuron • Reduces pain and makes one feel good • “Opiates” (heroin, codeine, morphine, oxycodone, hydrocodone, etc) – bind to endorphin receptors and mimic endorphins

Anandamide • Involved in working memory, regulation of feeding behavior, generation of motivation and pleasure • Anandamide receptors are called cannabinoid receptors – A lot of cannabinoid receptors in the hippocampus (short term memory), cerebellum (coordination) and basal ganglia (unconcious muscle movement) of brain • THC (found in marijuana) mimics anandamides and binds to cannabinoid receptors

Peripheral Nervous System • 12 pairs cranial nerves • 31 pairs spinal nerves

PNS Flow Chart Peripheral Nervous System Motor Sensory nerves Somatic nerves Autonomic nerves Sympathetic nerves Parasympathetic nerves

PNS cont. • Motor nerves are divided into – Somatic n. s. - conscious activities – Autonomic n. s. – unconscious activities • Autonomic n. s is divided into – sympathetic and – parasympathetic divisions.

PNS cont. SYMPATHETIC PARASYMPATHETIC • “fight or flight” responses • speeds up heart rate, breathing and other functions vital to survival • Digestion and other less essential functions will be slowed for awhile. • when the body is not mobilized and active in fight or flight. • speeds up digestion and other essential functions • When the body is in this mode, heart rate and breathing are calm.

The Central Nervous System • The Brain • The Spinal Cord

Central Nervous System - Spinal Cord Figs 11. 5, 11. 6, & 11. 7

Reflexes Fig. 11. 8

Central Nervous System: The Brain • Cerebrum – Largest part – Sensory & motor functions – Higher mental functions (memory, reasoning, etc) • Brainstem – Connects the cerebrum to the spinal cord • Cerebellum – Coordinates voluntary muscle movements • Diencephalon – Processes sensory info Fig. 11. 15

The Cerebrum • Divided into right and left cerebral hemispheres • Covered by folds called convolutions/gyri and grooves called sulci (little groves) and fissures (big grooves) • Connected by the corpus callosum • It has a cortex: an outer covering about 2 mm thick • Gray matter vs. white matter

The Cerebrum cont. • The cerebral cortex is divided into LOBES which control various functions • FPOT Fig. 11. 16 & 11. 17

The Cerebrum cont. • FRONTAL LOBE – – “Primary Motor Area” • controls voluntary muscles – “Broca’s Area” • motor speech • usually L hemisphere – Voluntary eye movement – Concentration, planning, problem solving, analysis

The Cerebrum cont. • PARIETAL LOBE – Sensory info: touch, taste, pressure, pain • interpretation of sensory info, “awareness” of body – “Wernicke’s Area” • sensory speech, understanding written & spoken language • usually L hemisphere

The Cerebrum cont. • OCCIPITAL LOBE – visual senses – analyzing visual patterns, combining visual images with other info (i. e. recognizing a person) • TEMPORAL LOBE – sensory smell and hearing – interpretation of sensory experiences (understanding speech, reading)

Cerebral Hemispheres • Hemisphere = half of sphere (brain) • The right side of the brain controls the left side of the body and vice versa • Corpus callosum

The Cerebellum • Integrates sensory info – Balance, coordination of skeletal muscle, posture

Brainstem Fig. 11. 21 • Brainstem: Connects the cerebrum to the spinal cord – Midbrain: visual and auditory reflex center – Pons: transfer nerve impulses – Medulla Oblongata: • Cardiac center- heart rate • Vasomotor centersmooth muscle in blood vessels/blood pressure • Respiratory centerbreathing rate • Coughing, sneezing, swallowing and vomiting reflexes

1. Thalamus- Diencephalon - Receives all sensory impulses (except smell) and relays them to the appropriate region of the cerebral cortex 2. Hypothalamus – – Maintain homeostasis – Links the nervous system to the endocrine system 3. Pituitary & pineal glands Fig. 11. 19

Diencephalon cont. • The limbic system is a collection of structures involved in emotional behavior and your feelings – Includes the amygdala and hippocampus

MEMORY • • Primarily occurs in the cerebrum and the hippocampus (in the diencephalon) 3 main types of memory: 1. Sensory memory = lasts momentarily and involves input from senses 2. Short term memory = lasts from a few seconds or minutes to hours (varies)

Memory cont. 3. Long term memory = the neurons actually change shape (dendrites extend, more are made, etc) and connect with other neurons. Lasts days to years (varies).