Bi 103 Notes: Chapter 34: The Nervous System

I. Neurons

A. Neurons = specialized “excitable cells” that allow for communication throughout the body via electrical impulses.

B. Neuron Anatomy & Function

1. dendrites

2. Cell body

3. Axon

4. Synaptic Terminals

C. Neurons transmit signals with Action Potentials (AP)

1. Resting membrane potential : - inside cell, + outside cell

2. In an AP, ion channels open in parts of the axon membrane, allowing a flip in membrane potential: + inside, - outside

3. AP’s are propagated down axons (“the wave”)

4. At synapses, electrical signal converted to chemical signal

D. Neurotransmitters (common)

1. Acetylcholine: activates skeletal muscle

2. Dopamine: Controls movement

3. Epinephrine: activates fight-or-flight response

4. Serotonin: Influences mood

5. Endorphins: Influences mood, reduces pain sensation

E. Information processing

1. Determine stimulus type (trace where AP comes from)

2. Signal intensity of stimulus

a) depends on # neurons responding

b) frequency of neuron signals

II. Organization of the Nervous System

A. Central Nervous system

1. Brain

2. Spinal Cord

B. Peripheral Nervous system

1. Motor Division

a. Autonomic

1. Sympathetic

2. Parasympathetic

b. Somatic

2. Sensory Division

III. Central Nervous system

A. Protection

1. bone: skull, vertebrae

2. meninges: triple layer connective tissue

a. spinal fluid for cushioning

3. blood brain barrier: selective lining on cranial blood vessels

B. Spinal cord

1. White matter: myelinated axons of neurons running up and down spinal cord

2. Gray matter: cell bodies of motor neurons & association neurons

3. Dorsal root: sensory neuron axons

4. Dorsal root ganglion: sensory neuron cell bodies

5. Ventral root: motor neuron axons

C. Brain

1. Hindbrain

a. Medulla: breathing, heart rate, bp

b. Pons: sleep transitions, stages

c. Cerebellum: coordinates movement

2. Midbrain

a. Visual/Auditory reflex centers (reflex movements of head)

b. Reticular formation: filters/controls arousal of brain

3. Forebrain

a. Thalamus:

1. relays info from body to limbic system & cerebral cortex

b. Limbic system

1. hypothalamus: homeostatic control

2. amygdala: pleasure, fear, rage

3. hippocampus: long term memory

c. Cerebral cortex

1. frontal lobe

2. parietal lobe

3. temporal lobe

4. occipital lobe

IV. Senses

A. Sensory receptors: detect signals, convert from one form to another.

1. Thermoreceptors: temperature

2. Mechanoreceptors: vibration, pressure, gravity, motion

3. Photoreceptors: light

4. Chemoreceptors: chemicals

5. Pain receptors: pain

B. Sound

1. Sound waves = vibrations (passed from outerà middleà inner ear

2. Hair cells = mechanoreceptors

C. Sight

1. Retina includes photoreceptors which excite optic nerve

a. Rods: very sensitive to light (not color)

b. Cones: color (red, blue, green) concentrated in fovea

D. Odor & Taste

1. Chemoreceptors bind to chemicals- in taste pores (taste)

2. Receptors for scent in olfactory epithelium

3. Primary tastes, majority of what we perceive as taste is from scent

E. Pain

1. Damaged cells spill chemicals

2. Released K+ ions stimulate pain receptors

3. Released enzymes produce bradykinin, which activates pain receptors