phys 2

Nervous System & Endocrine Study Guide

CHAPTER 7 – Neurons & Signaling

Nervous System Divisions

CNS (Central Nervous System)

• Brain

• Spinal cord

PNS (Peripheral Nervous System)

• All nerves outside CNS

Sensory (Afferent) pathway

• Carries signals TO CNS

Motor (Efferent) pathway

• Carries signals FROM CNS

Autonomic nervous system

• Involuntary

• We do not consciously control it

Neuron Structure

Axon hillock

• Contains many voltage-gated ion channels

• Site where action potentials start

• Summation of inputs occurs here

Myelination

Myelin

• Lipid insulation around axons

• Speeds up action potentials

PNS myelination

• Schwann cells

CNS myelination

• Oligodendrocytes

Glial Cells

Microglia

• Phagocytosis

• Immune defense

Ependymal cells

• Produce cerebrospinal fluid (CSF)

Membrane Potentials

Resting membrane potential (RMP)

• ~ -70 mV

Depolarization

• Membrane becomes less negative

Repolarization

• Membrane returns to resting potential

Hyperpolarization

• Membrane becomes more negative than -70

Ion Channels

Ligand-gated channels

• Open when neurotransmitter binds

• Example: Na⁺ channels

Mechanical-gated channels

• Respond to physical stimulus

• Example: bug crawling on arm

Leak channels

• Always open

• Not gated

Voltage-gated channels

Open when membrane potential changes

• Na⁺ channels → depolarization

• K⁺ channels → repolarization

Threshold ≈ -55 mV

Graded Potentials

Characteristics

• Can be depolarizing or hyperpolarizing

• Lose strength over distance

• Do not produce action potentials directly

But:

All action potentials begin from graded potentials

Action Potentials

All-or-nothing

Steps:

1. Depolarization
   

   • Voltage-gated Na⁺ channels open

   • Sodium rushes into cell

3. Peak

4. Repolarization
   

   • K⁺ channels open

   • Potassium leaves cell

6. Hyperpolarization

7. Return to RMP
   

   • Na⁺/K⁺ pump restores gradients

Refractory Period

Absolute refractory period

• During depolarization

• No new AP possible

Relative refractory period

• During hyperpolarization

• Requires stronger stimulus

Saltatory Conduction

Occurs in myelinated axons

Action potentials jump between nodes of Ranvier

Result:

• Much faster conduction

Synapse

Synapse

• Junction between neurons

Steps:

1. Action potential arrives

2. Ca²⁺ enters presynaptic neuron

3. Neurotransmitter released by exocytosis

4. Neurotransmitter binds receptors on postsynaptic cell

Neurotransmitters

Excitatory

Cause depolarization

Examples:

• Glutamate

• Acetylcholine (ACh)

Inhibitory

Cause hyperpolarization

Examples:

• GABA

Summation

Occurs at axon hillock

Temporal summation

• Rapid signals from one neuron

Spatial summation

• Signals from multiple neurons

CHAPTER 8 – Brain

Brain Structure

Gyri

• Bumps/folds on brain surface

Corpus callosum

• Connects left and right hemispheres

Gray matter

• Neuron cell bodies

• Superficial

White matter

• Myelinated axons

• Deeper

Lobes of Brain

Frontal lobe

• Decision making

• Precentral gyrus → motor cortex

Parietal lobe

• Sensory processing

• Postcentral gyrus → somatosensory cortex

Temporal lobe

• Hearing

Occipital lobe

• Vision

Insula

• Sensory processing of visceral organs

Language Areas

Broca’s area

• Motor speech production

Damage:

• Can’t form words

Wernicke’s area

• Speech comprehension

Damage:

• Can’t understand language

Diencephalon

Thalamus

• Sensory relay station

Hypothalamus

• Homeostasis

• Controls pituitary gland

Brain Stem

Parts:

• Midbrain

• Pons

• Medulla oblongata

Controls vegetative functions

Examples:

• Heart rate

• Breathing

• Blood vessel diameter

Reticular Activating System (RAS)

Promotes wakefulness and alertness

Sleep

Two main states:

REM sleep

• Dreaming

NREM sleep

• Stages 1–4

Controlled partly by circadian rhythm

Cerebellum

Second largest brain structure

Function:

• Coordination

• Balance

Damage causes:

• Ataxia (uncoordinated movement)

Spinal Cord

Functions:

Ascending tracts

• Sensory signals to brain

Descending tracts

• Motor signals from brain

Spinal Nerves

Contain both sensory and motor fibers

Dorsal root

• Sensory input

Ventral root

• Motor output

Reflex Arc

Example: Withdrawal reflex

Steps:

1. Pain receptor activated

2. Signal goes to spinal cord

3. Flexor muscles activated

4. Extensors inhibited

Spinal cord responds before brain

Autonomic Nervous System

Sympathetic

Fight or flight

• Short preganglionic

• Long postganglionic

Neurotransmitters:

• ACh → ganglion

• Norepinephrine → target

Parasympathetic

Rest and digest

• Long preganglionic

• Short postganglionic

Neurotransmitter:

• Acetylcholine

Important Drugs

Beta blockers

• Block sympathetic effects

Albuterol

• Beta agonist

• Opens airways

Atropine

• Blocks muscarinic receptors

• Causes pupil dilation

CHAPTER 10 – Sensory Systems

Sensation vs Perception

Sensation

• Detecting stimulus

Perception

• Interpreting stimulus

Steps of Perception

1. Stimulus

2. Transduction

3. Conduction

4. Perception in brain

Receptors

Chemoreceptors

• Smell, taste

Nociceptors

• Pain

Proprioceptors

• Body position

Receptor Types

Tonic receptors

• Do not adapt

• Example: pain

Phasic receptors

• Adapt quickly

• Example: clothing

Taste (Gustation)

Taste receptors detect:

• Salty → Na⁺

• Sour → H⁺

• Sweet → sugars

• Bitter → toxins

• Umami → proteins

Taste buds last ~10 days

Primary taste cortex:

• Insula

Smell (Olfaction)

Odor molecules must be:

• Water soluble

• Present in sufficient concentration

Smell strongly influences:

• Taste

• Memory

• Behavior

Vestibular System (Balance)

Located in temporal bone

Semicircular canals

• Detect head rotation

Hair cells

• Mechanoreceptors

Endolymph

• Fluid inside canals

Hearing

Sound waves cause:

1. Tympanic membrane vibration

2. Movement of bones:
   

   • Malleus

   • Incus

   • Stapes

4. Fluid movement in cochlea

5. Hair cells bend → nerve signal

Frequency = pitch

Amplitude = loudness

Vision

Eye Structures

Cornea

• Bends most incoming light

Lens

• Adjusts focus (accommodation)

Iris

• Controls pupil size

Retina

Three layers:

1. Photoreceptors

2. Bipolar cells

3. Ganglion cells

Photoreceptors

Rods

• Night vision

• Light sensitive

• Black/white

Cones

• Color vision

• High acuity

Colors:

• Red

• Green

• Blue

Dark vs Light Adaptation

Dark adaptation

• Regeneration of rod pigments

Light adaptation

• Breakdown of cone pigments

CHAPTER 11 – Endocrine System

Hormone Interactions

Additive

• Two hormones produce same effect

Complementary

• Different hormones contribute to same outcome

Permissive

• One hormone increases sensitivity to another

Antagonistic

• Opposite effects

Example:

• Insulin vs Glucagon

Hypothalamus & Pituitary

Hypothalamus controls pituitary through releasing hormones

Examples:

• GnRH

• TRH

• CRH

• GHRH

Anterior Pituitary Hormones

• FSH

• LH

• TSH

• ACTH

• Growth Hormone

• Prolactin

Posterior Pituitary

Releases hormones made in hypothalamus:

• ADH

• Oxytocin

Adrenal Gland

Adrenal Cortex

Produces steroid hormones:

Mineralocorticoids

• Aldosterone

• Na⁺ and K⁺ balance

Glucocorticoids

• Cortisol

• Glucose metabolism

Androgens

• Sex hormones

Adrenal Medulla

Releases:

• Epinephrine

• Norepinephrine

Part of sympathetic nervous system

Thyroid

Hormones:

• T3

• T4

Functions:

• Increase metabolism

• Increase sensitivity to catecholamines

Requires iodine

Thyroid Disorders

Hypothyroidism

• Low metabolism

• Can cause goiter

Hyperthyroidism

• Graves disease

• Bulging eyes

Parathyroid

PTH

• Increases blood calcium

Mechanism:

• Breaks down bone

Calcitonin

• Opposite effect

• Builds bone

Pancreas

Alpha cells

• Glucagon

• Raises blood glucose

Beta cells

• Insulin

• Lowers blood glucose

Insulin:

• Moves glucose into cells

• Stimulates glycogen storage

Pineal Gland

Secretes:

• Melatonin

Controls:

• Sleep cycle