DECONSTRUCTING THE NERVOUS SYSTEM

Smallest structural unit is the neuron


Glia are cells that support the neuron by
providing nourishment and insulation of the axon


Do not divide and aren’t replaced when they die
More numerous than neurons
Consists of 2 main divisions
NERVOUS SYSTEM DIVISIONS
Nervous System
Central Nervous
System (CNS)
Brain
Peripheral Nervous
System (PNS)
Spinal Cord
Autonomic
(involuntary)
Regulates internal
environment
Sympathetic
(Fight or flight)adrenergic
Somatic
(voluntary)
To and from skeletal
muscles
Parasympathetic
(Rest and digest)cholinergic
REFLEXES


Automatic responses to
stimuli, i.e knee-jerk
5 main
stages/components

Receptor


Sensory neuron


Spinal cord
Motor neuron


Signal towards CNS
Integration center


Detects stimuli
Signal exits CNS
Effector

Produces a response
to 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
AUTONOMIC NERVOUS SYSTEM
Parasympathetic
o Neurons from
brain and lower
spinal cord
o Synapse within
target organs
o
Sympathetic
o emerge from
middle of spinal
cord
o Synapse at
target organs
o Both cooperate
to maintain
homeostasis
o
THE HUMAN BRAIN

Brain is protected via
multiple structures

Blood brain barrier


Meningial layers


Selective permeability
Cerebrospinal fluid
 Cushions CNS and
provides nutrients
3 main regions

brainstem is pons,
medulla oblongata,
and midbrain
BRAIN STRUCTURE FUNCTIONS
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
o
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


Parietal lobe


Somatosensory cortex receives and integrates stimuli from
sensory systems
Temporal lobe


Motor cortex sends signals to muscles; higher order processes
Memory, hearing, and language
Occipital lobe

Vision
DECODING BRAIN STRUCTURES

Cerebellum


Brain stem


Alertness and attentiveness
Thalamus


Controls vision
Reticular formation


Controls smell
Optic bulb


Controls heart rate, breathing, and digestion; also emesis center
Olfactory bulb


Involved in coordination, balance, movement, posture, and
planning learned movements
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
SYNAPTIC COMMUNICATION
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
o
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)


Amino acids

Include aspartate, glutamate, glycine, and GABA


Dual roles as hormones (first 3)
First 2 excitatory and last 2 inhibitory
Soluble gases

Nitric oxide (NO)

Viagra promotes NO release into erectile tissue