The Nervous system

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 hormonesA cell with a single receptor on it

Does not bind,

No reactionGood 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.