Nervous System

Nerve Cell The nerve cell is the basic unit of communication in the vertebrate nervous system

Three Classes of neurons
The Neural circuit consists of
Sensory neurons
receptor for stimulus
Interneuron
integrate signals
Motor neuron
transfer signal to effector (muscle)

Anatomy of a Neuron
Cell body: functional portion
Dendrites: short extensions that receive signals
Axon: long extension that transmits impulses

How does a neuron hold and move info?
A neuron at rest has a voltage difference across the plasma membrane called a resting voltage potential
An action potential is when this charge across the membrane is briefly switched
The action potential moves down the membrane at a rapid pace.
Ap can move faster over mylenated portions is called saltatory conduction

How does a signal move from one neuron to another?
A synaptic cleft divides 2 neurons
The AP will not move across the synaptic cleft
Neuro transmitters are released by the signal cell to the receiver cell
Move by diffusion

Types of chemical synapse
Acetylcholine: neuromuscular junctions, glands, brain and spinal cord
Norepinepherine: affects brain regions concerned with emotions, dreaming

Paths of information flow
Signals between the brain and spinal cord move to the body regions by nerves
Sensory nerves move a signal towards the brain and spinal cord
Motor neurons move a signal from the brain or spinal cord to the body

Divisions of the nervous System
Central nervous system
CNS
Is the brain and spinal cord
Peripheral nervous system
PNS
all nerves that carry signals to and from the CNS

Parts of the PNS
Sensory Division carries info to the brain and spinal cord.
Motor Division carries info from the brain to the bodies effectors (things that do the work)

The Motor division of the PNS has 2 divisions
Somatic nerves relay commands to and from skeletal muscle
Voluntary control
Autonomic nerves send signals to and from smooth muscles
Involuntary control
Sympathetic
Parasympathetic

The autonomic divisions
Parasympathetic
slow down the body activity when the body is not under stress
Rest and digest
Sympathetic
increase overall body activity during times of stress, excitement or danger
fight or flight response
hormone epinephrine

Sympathetic and Parasympathetic
Are Antagonistic
Work towards the automatic, subconscious maintenance of homeostasis.

Components of the CNS
Spinal cord
31 pair of spinal nerves
Grey matter
White matter
Controls some reflex actions like bladder emptying
Brain parts
Hindbrain
medulla oblongata
cerebellum
pons
Midbrain
Forebrain
cerebrum
thalamus
hypothalamus

Other parts of the CNS
The two cerebral hemispheres communicate through the corpus collosum
left verbal skills
right nonverbal skills such as music math, abstract
Brain cavities and Canals
cerebrospinal fluid surrounds and fills in cavities in the brain
Blood Brain barrier- controls what moves into the brain. Will prevent infections.

Our state of consciousness
The CNS governs sleeping, dozing, daydreaming and full alertness
neurons of the reticular activating system control the changing levels of consciousness by releasing serotonin.

Limbic system
Involved in both memory and emotion.
Is involved with behavior.
Odors pass through this system and may influence or behavior and emotions.

Memory
Association is the linkage of information to structural and chemical changes
short term- few bits lasts a couple of hours
Long term- permanent and limitless
The most important info goes rapidly into long term storage
memory is stored in a form resistant to degradation
Possibly caused by changes in synapses.

Tips on studying
Concentrate on what you study.
Minimize interference.
Study takes time.
Break material into smaller portions.
Rephrase materials in your own words.
Test yourself to see what you know.

Disorders of the nervous system
Trauma
Infections
Transmission and synaptic defects.
Abnormal growth

Sensory Reception If a tree falls in the woods with no one to listen does it make a sound?

Receptors
Are the actual structures that respond to our environment.
Each receptor will respond to a different signal.
Essentially translators, they translate an energy into one that can be perceived by the brain.

Sensory systems consist of
Each system has 3 parts
1) sensory receptors.
2) pathway to the brain.
3) region of the brain that recognizes this section.

Types of sensory Receptors
Chemoreceptors
Mechanoreceptors
Thermoreceptors
Nociceptors
Photoreceptors
olfaction and taste
touch, stretch, hearing, equilibrium
radiant energy, infared
pain receptors
light

Sensory Pathways
If a receptor is stimulated enough it results in an action potential.
The action potential reaches the brain.
The stronger the stimulus the greater number of action potentials reach the brain.
Sensory adaptation is when the action potentials are reduced by a constant stimulus.
Certain receptors will not adapt.

Somatic sensations
Touch & Pressure
Temperature
Pain
Muscle sense
Mechanoreceptors that respond to changes or constant pressure
Increase in temperature causes and increase in AP
Respond to intense stimulus on other receptors, cannot be ignored
Mechanoreceptors give measurement as to the location of all the muscles and bones in a given moment.

Limb position, length and tension
How do we know where we are at?

Referred pain

Taste and Smell
Gustation : Taste
Receptors located on tongue, roof of mouth, throat and palate
Four tastes
sweet
sour
bitter
salty
Olfaction : smell
detect chemicals
olfactory bulbs in brain interpret smell
smell is often combined with emotion

Taste
Taste Bud 25 cells
Taste hairs project into mouth
Hairs contain receptors
Categories
Sweet
Sour
Salty
bitter

Hearing
Acoustical receptors detect vibrations
The ear
In the organ of corti loudness is determined by The total number of cells that are stimulated
Pitch depends on frequency of vibration

Balance
Vestibular apparatus
Closed system of fluid filled sacs
Contain otoliths that detect changes in orientation as well as acceleration
Overstimulation of the hair cells of the vestibular apparatus results in motion sickness

Vestibular apparatus

The Eye

Structure of the eye
Outer sclera (white) (is all the way around)
Cornea (clear)
Pupil (opening to the back)
Lens (transparent)
Retina (back side has photoreceptors and support material)
Fovea has highest concentration of photoreceptors.

Regulating light amount
The iris adjusts to amount of light entering the eye.
The lens goes through accommodation to adjust lens curvature (as we age the lens cannot buldge enough to focus on a close object)

Light must reach the sensors by going through neurons.
Outermost layer is pigmented to absorb light not absorbed by the sensors
Photoreceptors are in middle layer
Translucent neurons and ganglions are on top of the photoreceptors.

Production of Action Potentials by Rods and Cones
Within these cells flattened disks contain photopigment
When this protein absorbs light it changes conformation, if enough are activated they cause an action potential.
Rods contain rhodopsin and are most sensitive to dim light
Cones contain different pigments

Rods and Cones
Bright light tends to use more cones, 300x more sensitive
Dim light uses Rods and Rhodopsin, it is broken apart by light and must be remade (hence the 5-10 minute wait to see in darker areas)

Signaling to visual perception
Photoreceptors are in the retina
When rods or cones are stimulated they send a signal to the brains visual cortex.
In the brain the final interpretation makes sense of sight

Problems with the Eyes
Retinal detachment: retina separates form choroid
Cataracts: lens becomes opaque
Color blindness: Inability to distinguish colors, is a genetic disease, lacks specific types of cones

The Endocrine system The oldest method of control is using a signal molecule that moves from one part of the body to the other

The Endocrine System Regulates
Salt and water balance
Blood pressure
Stress responses
Digestion
Cellular metabolism
Production of RBC’s
Growth and development

Location of Endocrine Glands

Hormones and other signal molecules
Hormones : molecules secreted by glands into the blood that move to a nonadjacent target
Neurotransmitters : act on a directly adjacent cell
Local signaling molecule : act quickly and degrade quickly
Pheromones : secreted by glands and target cells in other organisms

Signaling Mechanisms
Requirements
Cells that secrete the signal molecule are either within a gland or nervous tissue
The signal molecule
Steroid hormone (fat soluble will move through the plasma membrane)
Non steroid hormone (peptides and other molecules must bind to a receptor on the cell)
Target cell

Target cell activities
Different hormones activate different cellular response mechanisms
No all cells have receptors for all hormones:
Three possible hormones A cell with a single receptor on it Does not bind, No reaction Good fit rx occurs

Characteristics of the Endocrine system
Each hormone acts only on certain cells
Cells respond only when they have receptors
Is slower than nervous system control
Endocrine and nervous system to interact with one another.

Interaction of Endocrine System and Nervous System

Negative Control using Hormones

The pancrease an endocrine and an exocrine gland
Glucagon: raises blood sugars, release of stores and AA metabolism
Insulin: lowers blood sugars opposes glucagon
Somatostatin: inhibits secretion of the above enzymes

Bracketing using hormones

Regulation of Blood Calcium concentration
Increase Calcium
Parathyroid Hormone: removes calcium and phosphate from bone, increase absorption, retention of calcium in kidneys
Decrease of Calcium
Calcitonin

Oxytocin and nursing, a cascade of events
At the end of pregnancy, Estrogen rise.
Uterus produces more oxytocin receptors
Fetus produces oxytocin, starts a cycle of material production of oxytocin
Oxytocin is a part of the neuroendocrine reflexes and will help in the smooth muscle contractions which cause the release of milk.

Nervous System

by Junhel Dalanon on Feb 26, 2010

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Nervous System — Presentation Transcript