Nervous System -> Physiology

Chapter 8

Sensory Neurons

→ afferent

→ sensory neurons receive information from other enurons monitoring the internal and external environment

→ has two types

→ Somatic and Visceral

Somatic Sensory Neurons

→ external receptors

→ external environment

→ touch, taste, pressure, proprioceptors, etc.

Visceral Sensory Neurons

→ internal environment

→ monitor internal organs (digestive, respiratory, urinary, etc)

→ feelings of distention, deep pressure, and pain

Motor Neurons

→ efferent neurons

→ carry information from the CNS to the body

→ two groupings, somatic and visceral

Somatic Motor Neurons

→ innervate skeletal muscles

→ control voluntary movements

Visceral Motor Neurons

→ innervate all other effectors including smooth and cardiac muscle as well as glands

→ controls involuntary functions like digestion and heart rate

Interneurons

→ association neurons

→ only found in the brain and spinal cord

→ connect other sensory and motor neurons

→ by far the most numerous type at about 20 billion

→ play a role in all higher functions

Primary Role of Neuroglia

→ support neurons

→ maintain homeostasis, form myelin, and provide protection

→ four categories in CNS

→ two in PNS

Astrocytes

→ maintain blood-brain barrier

→ regulate nutrient and ion concentrations, provide structural support, and assist in repair and scarring of the brain and spinal cord

→ CNS

Oligodendrocytes

→ adds myelin to axons in CNS

→ provides insulation and increases the speed of electrical signals

→ CNS

Microglia

→ phagocytic

→ immune defense of the central nervous system, removing debris and dead cells

→ CNS

Ependymal

→ have cilia

→ produce and move cerebral spinal fluid (CSF)

→ line the ventricles of the brain and central canal of the spinal cord

→ CNS

Satellite Cells

→ support neurons

→ regulate exchange of materials

→ surround and support neuron cell bodies

→ similar in function to the astrocytes in the CNS

→ PNS

Schwann Cells

→ cover axons outside the CNS

→ PNS

Sodium Potassium Pump

→ kicks three Na+ outside and takes in two K+

→ charge discrepancy where inside is less positive

→ creates a forced concentration gradient where the concentration of sodium is higher outside the cell and the concentration of potassium is higher inside the cell

→ when the cell receives a sign, it opens a single Na+ channel

→ causes the cell to flood with sodium and make the cell more positive

→ charge travels along the axon, unlocking more Na+ channels

→ when it reaches the end, the signal has been sent

→ at this point in time, K+ is escaping the cell through K+ channels that opened at the same time as the Na+ channels

→ the cell needs a bit of time to recharge after a signal is sent

Membrane Potential

→ charge that results that results from the separation of charges inside and out the membrane

→ excessive positive charges on the outside of the cell

→ excessive negative charges on the inside of the cell

Resting Membrane Potential

→ membrane potential of undisturbed cell

→ __________ of neuron is -70mV

Point 1

→ graded depolarization brings area of excitable membrane to threshold

→ -60mV

Point 2

→ voltage-gated sodium channels open and sodium ions move into the cell

→ +30mV

Point 3

→ sodium channels close, voltage-gated potassium channels open

→ potassium ions move out of the cell

→ repolarization begins

Point 4

→ potassium channels close

→ both sodium and potassium channels return to their normal states

Axon Hillock

→ first part of axon to reach threshold

→ closest part of the axon to the main cell body

Resting Potential

→ axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels

→ channels are closed when membrane is at ______

Depolarization

→ shift towards 0mV

→ sodium rushes into the cell

→ potential becomes more positive

Approaching +30mV

→ sodium channels close

→ potassium channels open

→ less sodium enters the cell

→ potassium leaves the cell

→ makes the cytosol negative

Hyperpolarization

→ membrane potential -90mV

→ closing of potassium channels until resting is reached

Graded Potential

→ aka local

→ changes in the membrane potential that cannot spread from site of stimulation

→ occur in the plasma membranes of all cells

→ can trigger specific functions in small cells (glands)

→ can only activate large neurons if leads to the production of action potential

Action Potentials

→ change in membrane potential of excitable cells

→ excitable cells are the ones that have voltage-gated channels that open or close in response to ______

Nerve Impulse

→ change in membrane potential that travels the entire length of the cell

Threshold

→ level of depolarization needed to cause the action potential

Refractory Period

→ membrane does not respond to stimulus while recovering

Continuous Propogation

→ chain reaction that reaches the most distant part of the membrane

Saltatory Propagation

→ a potential skips over the myelinated portions of the axon

Continuous Propogation along an Unmyelinated Axon

→ as action potential develops at the initial segment, the membrane potential at this side depolarizes to +30mV

→ as the sodium ions entering at 1 spread away from the open voltage-gates channels, a graded depolarization quickly brings the membrane in segment 2 to threshold

→ an action potential now occurs in segment 2 while segment 1 begins repolarization

→ as the sodium ions entering at segment 2 spread laterally, a graded depolarization quickly brings the membrane in segment 3 to threshold and the cycle is repeated

Saltatory Propagation along a Myelinated Axon

→ an action potential develops at the initial segment

→ a local current produces a graded depolarization that brings the axon membrane at the next node to threshold

→ an action potential develops at node 2

→ a local current produces a graded depolarization that brings the axon membrane at node 3 to threshold

Epinephrine

→ commonly known as adrenaline

→ fight or flight neurotransmitter

→ produced in stressful or exciting situations

→ increases heart rate and blood flow

→ leads to physical boost and heightened awareness

Dopamine

→ pleasure neurotransmitter

→ feelings of pleasure, addiction, movement, and motivation

→ repeat behaviors that lead to _______ release

→ reward system

Serotonin

→ contributes to well-being & happiness

→ mood neurotransmitter

→ helps sleep cycle & digestive system regulation

→ affected by exercise & light exposure

→ passive transmitter

GABA

→ calming neuro transmitter

→ calms firing nerves in CNS

→ high levels improve focus

→ low levels cause anxiety

→ contributes to motor control & vision

Acetylcholine

→ learning neurotransmitter

→ involved in thought, learning, & memory

→ activates muscle action in the body

→ associated with attention and awakening

Glutamate

→ memory neurotransmitter

→ most common brain neurotransmitter

→ involved in learning & memory

→ regulates developments & creation of nerve contacts

Endorphins

→ euphoria neurotransmitters

→ released during exercise, excitement & sex

→ producing well-being & euphoria

→ reduces pain

→ biologically active section shown

Messages Sent Between Neurons

→ action potential arrives and depolarizes the axon terminal

→ extracellular Ca2+ enters the axon terminal triggering the exocytosis of ACh

→ ACh binds to receptors and depolarizes the postsynaptic membrane

→ Ach is removed by AChE

Depolarization Triggers

→ usually ACh and NE trigger _______

→ increases the probability of reaching threshold

→ excitatory effect

Hyperpolarization Triggers

→ usually dopamine, GABA, and serotonin trigger ______

→ moves membrane potential farther from threshold

→ an inhibitory effect

Excitatory vs. Inhibitory Neurotransmitter

→ A triggers depolarization

→ B triggers hyperpolarization

→ same neurotransmitter can have different effects at different synapses depending on the receptors

Postsynaptic Neuron Response

→ multiple presynaptic neurons can synapse with one postsynaptic neuron

→ has cumulative effects

→ if all release excitatory = action potential is triggered

→ if all release inhibitory = no action potential can occur

→ if half and half = cancel each other out, no action

Alpha Waves

→ characteristic of normal resting adults

Beta Waves

→ accompany intense concentration

Theta Waves

→ seen in children and frustrated adults

Delta Waves

→ occur in deep sleep and in certain pathological conditions

Fact Memory

→ specific bits of information

Skill Memories

→ learned motor skill that can become incorporated into unconscious memory

Short-Term Memories

→ do not last long but can be recalled immediately

→ converting into long-term memory through memory consolidation

Long-Term Memories

→ remain for long periods, sometimes an entire lifetime

Amnesia

→ memory loss as a result of disease or trauma

Basal Nuclei

→ masses of gray matter that lie beneath the lateral ventricles

→ function in subconscious control of skeletal muscle tone and coordination of learned movements

Limbic System

→ includes various areas of the cerebrum and diencephalon

→ a functional grouping rather than an anatomical grouping

→ includes amygdala, hippocampus, and hypothalamic

→ establishes the emotional states

→ links the conscious with the unconscious functions

→ aids in long-term memory storage and retrieval with help of the hippocampus

Parts of the Limbic System

→ amygdaloid bodies

→ hippocampus

→ hypothalamic centers

Amygdaloid Bodies

→ regulate heart rate, control fight or flight, link emotions with memory

Hippocampus

→ helps in learning and sorting memories

Hypothalamic Centers

→ emotional states and reflexes

Reflex

→ rapid, automatic response to a specific stimulus

→ predictable response every time

Simple Reflex

→ monosynaptic

→ sensory neuron meets motor neuron

→ only one synapse

Complex Reflex

→ interneuron between sensory and motor neurons

→ more than one synapse

Reflex Arc

→ wiring of a single reflex

→ arrival of stimulus and activation of receptor

→ activation of a sensory neuron

→ information processing in the CNS

→ activation of a motor neuron

→ response by peripheral effector

Babinski’s Reflex

→ triggered by stroking an infant’s sole

→ results in toe fanning

Plantar Reflex

→ triggered by stroking an adult’s sole

→ results in curling of toes

ANS Sympathetic Divison

→ located between T1 and L2 of the spinal cord

→ stimulates tissue metabolism

→ increases alertness

→ prepares individual for physical activity

→ stimulates sweat glands

→ stimulates erector pili muscles

→ reduces circulation to the skin

→ releases stored lipids

→ dialates pupils

ANS Parasympathetic Division

→ rest and repose

→ conserves energy and promotes sedentary activities

→ constricts pupils

→ increases digestion

→ stimulates defecation and urination

→ constricts respiratory passageways

→ reduces heart rate

→ reduces force of cardiac contractions

Relationship between Sympathetic and Parasympathetic Divisions

→ some organs innervated by only one division

→ most organs have dual innervation

→ mostly have antagonistic effects

Aging and the Nervous System

→ age-related changes begin by age 30 and accumulate over time

→ reduction in brain size and weight

→ reduction in number of neurons

→ decrease in blood flow to the brain

→ change in synaptic organization of the brain

→ increase in intracellular deposits and extracellular plaques

→ loss of neuron connections

→ dementia can be a result of all these changes