Ch. 35 The Nervous System

Nervous System

1. Neuron - basic unit of structure and function

2. Basic unit of neuron

a.) dendrite

b) cell body (soma or cyton)

c) axon

3. The 3 functional kinds of neurons

a) sensory (afferent) - receptor neurons carry impulses to brain and spinal cord (CNS)

b) motor (efferent) - effector neurons carry impulses from CNS to effector (muscle or gland)

c) interneuron (associative) - connector neurons found within CNS; transmit impulses between sensory, motor, and other interneurons

SENSORY NEURON (AFFERENT)

MOTOR NEURONS (EFFERENT)

INTERNEURONS (IN CNS!)

4. Nerve - an organ composed of:a) many hundreds, thousands of neuronsb) other tissues - epithelium, connective, blood vessels

5. 3 functional types of nerves a) sensory nerve - consists of sensory neurons- auditory Receptor CNS(brain, spinal cord)- optic (ear, eye, skin)b) motor nerve - consists entirely of motor neurons [ex:CNS effector

(muscle or gland)]c) mixed nerve - consists of both sensory and motor neuron bundles -

neurons separated by connective tissues (spinal cord - all 31 pairs of spinal nerves)

NERVE

Motor Neuron - Longitudinal View

1. Dendrites - transmit impulses toward cell body

2. Nucleus - essential to cell functions

3. Cell body - synthesizes the neurohumor or neurotransmitter (adrenaline, acetylcholine)

4. Neurofibrils - protein tubules which carry impulses throughout cell

5. Schwann cell - cell around axon - membrane (neurilemma) essential to regeneration of neuron

6. Myelin sheath - lipid layer around axon; an insulator and also increases rate of impulse conduction

7. Axis cylinder - composed of neurofibrils - carry impulses throughout neuron

8. Nodes of Ranvier - spaces between Schwann cells

9. Motor end plate - (axon terminals) site where neurotransmitters (neurohumor) are stored and released into synapse or effector

10. Axon - carry impulses away from cell body to synapse or to effector

Stimulus- Impulse1. Stimulus - environmental change which

causes a response; usually a form of energy

a) radiant (heat, light) d) sound

b) electrical e) chemical

c) pressure

2. Impulse - electrochemical change along a neuron

3. Threshold level stimulus- minimum strength stimulus needed to initiate nerve

impulse (varies for different neurons and individuals)

4. Nerve Impulse - “All or None” (Property of neurons)

- Once impulse is initiated by threshold stimulus the neuron responds 100%

- Impulse travels through the cell at the same rate and same strength

Section 35-2

Figure 35-7 An Impulse

NERVE IMPULSE

6. Refractory period - lapse of time required for neuron membrane to restore original charge (at this time the cell area is insensitive to another stimulus)

7. Human refractory periods (wide range)

a) slowest neurons - longest refractory periods 1/250 sec. --- can transmit 250 impulses per second

b) most rapid neurons - 1/2500 sec. --- can transmit 2500 impulses per second (shortest refractory time)

8. Rate of impulse conduction (dependent on 2 factors)

a) diameter of neuron - the larger the cell diameter, the faster the rate

b) myelin - myelin sheath enhances rate– non-myelinated cells - slowest conduction rate

(sensory neurons) – myelinated cells (motor) - faster rates

9. At axon terminal of neuron - axon stores and releases neurotransmitter (NT) into adjacent tissues:

a) effector - muscle or gland

b) synapse - neurotransmitter either activates or inhibits adjacent neuron

10. Activation of cell

- Occurs when NT makes adjacent neuron membrane more permeable to Na+

- Impulse initiated

11. Inhibition of cell

- Occurs when NT makes adjacent neuron (postsynaptic) membrane less permeable to Na+

- More permeable to Cl- and K+

- Adjacent cell membrane hyperpolarized

Section 35-2

Figure 35-6 Resting Potential

RESTING POTENTIAL (POLARIZED)

RECAP: NEURONAL CELL MEMBRANE TRANSPORT

• ACTIVE TRANSPORT: SODIUM- POTASSIUM PUMP; NEEDS ATP; AGAINST CONC. GRADIENT (LOW HIGH)

• PASSIVE TRANSPORT: SODIUM & POTASSIUM CHANNELS (GATES); FACILITATED DIFFUSION; NO ATP; WITH CONC. GRADIENT (HIGHLOW)

- Bell-Magendie Rule= IMPULSE AT SYNAPSE TRAVELS IN ONE DIRECTION

- From axon of presynaptic neuron to dendrites/ cell body of postsynaptic neuron

- Only axon end of neuron stores neurotransmitter

12. 4 Major types of Neurotransmitters

a) Acetylcholine (Ach) - motor neurons

b) Adrenalin(epinephrine) - motor, sensory, and associative

c) Noradrenalin (norepinephrine) - motor, sensory, associative

d) Seratonin - associative neurons

Vesicle

Axon

Axon terminal

Synaptic cleft

Neurotransmitter

Receptor

Dendrite of adjacent neuron

Direction of Impulse

Section 35-2

• NEUROTRANSMITTER ACTIVATES OR INHIBITS ADJACENT NEURON

• ANESTHESIA:

1. PREVENTS OPENING OF SODIUM GATES

2. BLOCK RECEPTORS ON POSTSYNAPTIC NEURON

SYNAPSE

1. SPINAL CORD- LARGE MIXED NERVE

A. WHITE MATTER- OUTER PORTION OF MYELINATED FIBERS RUNNING UP AND DOWN (TO & FROM BRAIN!)

B. GRAY MATTER- CELL BODIES OF ASSOCIATIVE & MOTOR NEURONS1. 31 PAIRS OF SPINAL NERVES (MIXED) – SENSORY FIBERS ENTER DORSAL ROOT, MOTOR LEAVE VENTRAL ROOT

• DESTRUCTION OF DORSAL ROOT – LOSS OF SENSATION IN PARTS THAT SUPPLYSENSORY NEURONS

• DESCRUCTION OF VENTRAL ROOT – MUSCULAR PARALYSIS OF BODY PART SUPPLIED BY MOTOR NEURON

• 2 MAIN FXN OF THE SPINAL CORD:1. COORDINATING CENTER – REFLEXES (MOST, LIKE KNEE JERK)2. CONNECTS PNS TO BRAIN

Spinal nerve

Central canalGray matter

White matter

Meninges

Section 35-3

Cross Section of the Spinal Cord

Pons

Pituitary gland

Hypothalamus

Cerebrum

Medulla oblongata Spinal cord

Cerebellum

Pineal gland

Thalamus

Figure 35-9 The Brain2. BRAIN (MENINGES, CSF)- 4 VENTRICLES (FLUID CIRCULATES W/IN CAVITIES)- 12 PRS. CRANIAL NERVES- 2 LARGE HEMISPHERES (LONGITUTINAL HALVES)- 3 REGIONS (FORE-, MID-, & HINDBRAIN)

1. HINDBRAIN A. MEDULLA OBLONGATA (BRAINSTEM)

• ESSENTIAL TO LIFE (VITAL CENTER)

• BREATHING RATE (VAGUS & PHRENIC NERVES)

• HEART RATE• BLOOD PRESSURE• SWALLOWING, VOMITING,

COUGHING CENTER

STRUCTURAL DIVISIONS OF HUMAN BRAIN

B. CEREBELLUM• “LITTLE BRAIN”- LARGEST

SEGMENT OF HINDBRAIN• CENTER FOR BALANCE &

COORDINATION• COORDINATES MUSCLE

ACTIVITY• COORDINATES IMPULSES

FROM EYES & SEMICIRCULAR CANALS TO MAINTAIN BALANCE (EQUILIBRIUM)

C. PONS (“BRIDGE”)• CARRIES IMPULSES

FROM ONE SIDE OF CEREBELLUM TO THE OTHER

• COORDINATES LEFT SIDE OF BRAIN WITH RIGHT

2. MIDBRAIN

• BETWEEN CEREBELLUM AND PONS – SLIGHTLY ABOVE

• CONTROLS SENSORY PROCRESSES

3. FOREBRAIN

a.HYPOTHALAMUS (HOMEOSTATIC CENTER)

REGULATES:• BODY TEMP• WATER BALANCE• FOOD INTAKE• GASTRIC SECRETION• ANTERIOR PITUITARY

GLAND WITH RELEASING HORMONES

)b. PITUITARY (HYPOPHESIS)

• ENDOCRINE GLAND THAT SECRETES HORMONES THAT MAINTAIN HOMEOSTASIS

• HAS ANTERIOR & POSTERIOR LOBES

C. THALAMUS• RELAY CENTER B/W

BRAINSTEM & CEREBRUM (B/T SENSE ORGANS & CEREBRUM

• REGULATES STATES OF SLEEP AND WAKEFULNESS

D. CEREBRUM• SETS MAN APART FROM OTHER

VERTEBRATES!• LEARNING, REASONING, MEMORY,

JUDGEMENT• SPEECH:

1. BROCA’S AREA – MOTOR

2. WERNICKE’S AREA – COMPREHENSION OF SPOKEN OR WRITTEN LANGUAGE

• LEFT BRAIN: SPEECH, LOGIC, WRITING, MATH

• RIGHT BRAIN: DISCRIMINATION OF SHAPE & FORM

E. CORPUS CALLOSUMCONNECTS RIGHT & LEFT CEREBRAL HEMISPHERES

Concept Map

which consists of

is divided into

that make up

which is divided into

Section 35-3

The Nervous System

Sensory nerves

Motor nerves

Autonomic nervous system

Somatic nervous system

Central nervous system

Peripheral nervous system

Sympathetic nervous system

Parasympathetic nervous system

AUTONOMIC NERVOUS SYSTEM

• CHECK & BALANCE SYSTEM THAT MAINTAINS HOMEOSTASIS (ANTAGONISTIC TO ONE ANOTHER)

• 2 DIVISIONS:

1. SYMPATHETIC

2. PARASYMPATHETIC• FIGHT-FLIGHT RXN:

NERVOUS CONTROL EVOKES THESE RXN’S RAPIDLY IN TIMES OF DANGER/STRESS.

HORMONES PROVIDE A BACKUP THAT CAN MAINTAIN A RESPONSE FOR A LONGER PERIOD.

AUTONOMIC NERVOUS SYSTEM

REFLEX ARC

REFLEX ARC