DECONSTRUCTING THE NERVOUS SYSTEM

Smallest structural unit is the neuron Do not divide and aren’t replaced when they die

Glia are cells that support the neuron by providing nourishment and insulation of the axon More numerous than neurons

Consists of 2 main divisions

NERVOUS SYSTEM DIVISIONS

REFLEXES

Automatic responses to stimuli, i.e knee-jerk

5 main stages/components Receptor

Detects stimuli Sensory neuron

Signal towards CNS Integration center

Spinal cord Motor neuron

Signal exits CNS Effector

Produces a responseto stimuli

THE INCREDIBLE EDIBLE NEURON Cell body

Stores the organelles, including the nucleus, and neurotransmitters

Dendrites Receive signals and conveys information to cell body Highly branched and often shorter (than axon)

Axon Transmits signals to other cells

Coated in a thick insulating material called myelin sheath Each is a Schwann cell and the spaces between are nodes of

Ranvier Only place where axon is leaky Salutatory conduction

Multiple sclerosis (MS) immune system destroys myelin Singular and longer

Synaptic terminal, branched end of axon that meets other cells Forms a synapse or point of communication between

cells

AU

TO

NO

MIC

NER

VO

US

S

YS

TEM

o Parasympathetico Neurons from brain and lower spinal cordo Synapse within target organs

o Sympathetico emerge from middle of spinal cordo Synapse at target organso Both cooperate to maintain homeostasis

THE HUMAN BRAIN

Brain is protected via multiple structures Blood brain barrier

Selective permeability Meningial layers

Cerebrospinal fluid Cushions CNS and

provides nutrients

3 main regions brainstem is pons,

medulla oblongata, and midbrain

BR

AIN

STR

UC

TU

RE

FU

NC

TIO

NS

o Biological clock is regulated by the suprachiasmatic nucleus (SCN) responding to visual input to maintain circadian rhythms

o Maintained without external clues

o Cerebrum has 2 hemispheres, connected by the corpus callosum

oControl opposite sides of body

CEREBRAL CORTEX Convolutions maximize

neurons in limited space

Responsible for human traits

Receives stimuli from all senses

Regulates voluntary movements

4 lobes Frontal, (2) parietal, (2)

temporal, and occipital Each with specialized

functions Association areas where

higher order processes occur, ‘thinking’

DECODING LOBES OF THE BRAIN Cerebral hemispheres demonstrate lateralization

Left=objective (language and logic) Right=subjective (creative endeavors)

Frontal lobe Motor cortex sends signals to muscles; higher order

processes Parietal lobe

Somatosensory cortex receives and integrates stimuli from sensory systems

Temporal lobe Memory, hearing, and language

Occipital lobe Vision

DECODING BRAIN STRUCTURES Cerebellum

Involved in coordination, balance, movement, posture, and planning learned movements

Brain stem Controls heart rate, breathing, and digestion; also emesis

center Olfactory bulb

Controls smell Optic bulb

Controls vision Reticular formation

Alertness and attentiveness Thalamus

Relays sensory info to cortex and multiple sensations Hypothalamus

Controls ANS, pituitary, and regulates brainstem

TURKEY MAKES ME SLEEPY

Arousal is a state of awareness while sleep is external stimuli that isn’t consciously perceived

Multiple brain areas contribute Reticular formation receives sensory info and

determines what reaches the cortex for processing More info = more alert and aware Can filter out repetitive stimuli

Pons and medulla promote sleep with stimulation 5-HT may be a neurotransmitter (milk before bed or

turkey = tryptophan) Midbrain causes arousal

Sleep is ESSENTIAL for survival and is an ACTIVE state for the brain

SLEEP CYCLE

I REMEMBER LEARNING TO CRY

Limbic system controls memory, learning, and emotion Include thalamus, hypothalmus, amygdala, and

hippocampus Attaches ‘feelings’ to basic survival mechanisms Memory is ability to store and retrieve

information from experience Amygdala adds emotion, acts as a filter for

remembering Hippocampus helps form and recall memories Factual and procedural memories differ

Odors or music can trigger memories

DISEASES OF THE BRAIN Schizophrenia

Lose the ability to distinguish reality Strong genetic component Treatments focus on DA, but can induce Parkinson symptoms

Depression Major depression and bipolar disorder Sadness that interferes with normal life and extreme mood swings Genetic component 5-HT imbalance so SSRI’s (Prozac, Paxil, and Soloft) prescribed

Alzheimer’s Disease Dementia characterized by confusion and memory loss Progressive disease that is hard to diagnose while alive

Tangles and plaques trigger neuronal death, but cause or symptom? Parkinson’s Disease

Difficulty in initiating movement and slowness of movement Progressive disease where age increases risk No cure, but treatments with DA to alleviate

COMPARATIVE NEURAL ANATOMY

Cnidarians are 1st phyla to evolve a nervous system Radially symmetrical adults have symmetrical nervous systems Control digestive cavity contractions and tentacle movement

Bilateral symmetry usually demonstrate cephalization, nervous system concentration in the head and centralization, presence of CNS and PNS

Platyhelminthes with nerve cords to control animal movements is simplest

Subsequent phyla see an increase in neuron number and segmentation

MEMBRANE POTENTIALS Potential energy (PE) that exists as electrical

charge across the neuron’s PM Cytoplasm charge = (-) charge, extracellular fluid =

(+) charge Stored by holding opposite charges apart across the

PM Results in the resting potential (-70 mV)

Ionic differences of intra- and extracellular fluid produce electrical differences or voltage Potassium (K+) is high inside, sodium (Na+) is high

outside cell K+ diffuses out readily through K+ channels, leaving a

(-) charge inside Na+-K+ pump maintains by moving Na+ out and K+ in

Can change with changing permeability to ions

SY

NA

PTIC

C

OM

MU

NIC

ATIO

N

o Can be electrical or chemical

o Electrical are found in the heart and digestive system, where steady rhythms are necessary

o Chemical release neurotransmitters stored in synaptic vesicles into the synaptic cleft

o Resulting events vary amongst synapse types

NEUROTRANSMITTERS Small molecules that

serve as chemical signals

Can be excitatory, inhibitory, or both Depends on action at

synapse and can vary in magnitude Excite if opens Na+

channels (flow into cell) Inhibit if open chloride

(Cl-) or K+ channels (flow in or out respectively)

Cell bodies can and often do receive both at 1 time Summation of signals

produces all-or-none response

TYPES OF NEUROTRANSMITTERS Acetylcholine (ACh) is excitatory and

inhibitory Contracts skeletal muscles, but relaxes cardiac Botulinum toxin (Botox) inhibits Ach so muscles in

eyes/mouth stop contracting = no wrinkles Monoamines have multiple roles in CNS

Include epinephrine (EPI), norepinephrine (NE), serotonin (5-HT), and dopamine (DA) Dual roles as hormones (first 3)

Amino acids Include aspartate, glutamate, glycine, and GABA

First 2 excitatory and last 2 inhibitory Soluble gases

Nitric oxide (NO) Viagra promotes NO release into erectile tissue