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:– CNS Body

Fig. 10.2

2 Different Types of Motor Nerves

• Somatic NS– consciously controlled

effectors

• Autonomic NS– involuntary effectors

Cells of the Nervous System

• NEUROGLIAL CELLS

• NEURONS vs.

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 RanvierFig. 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”

• Neuron = a cell• Nerve = bundles of

neuron axons, and neuroglial cells bound together– outside brain/spinal

cord

Fig. 11.24

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

• Passive pumps– with the gradient

Fig. 10.13

Na+/K+ Pump

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 & Adderall- increase

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 nerves

Somatic Autonomic nerves nerves

Sympathetic Parasympathetic nerves 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 • “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.

PARASYMPATHETIC • 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

Figs11.5, 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• 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 center-

smooth muscle in blood vessels/blood pressure

• Respiratory center- breathing rate

• Coughing, sneezing, swallowing and vomiting reflexesFig. 11.21

Diencephalon1. Thalamus-

- 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).