Nervous System

Purpose

• Communication

• Control

• Process information

• Gather information

Neuron

• Cell body– Contains nucleus and most normal cell functions– Receives chemical signal from adjacent neuron

• Axon– Transmits electrical impulse to synaptic terminals

• Synaptic terminals– Transmits chemical signal to cell body of adjacent

neuron

Types of Neurons

Synapse structure and function

Synapse close-up

Synapse receptors

Membrane Potential

• Inside of every cell is negative compared to the outside– Inside

• Anions – proteins, amino acids, sulfate and phosphate• Cations – potassium (K+)

– Outside• Anions – chloride (Cl-)• Cations – sodium (Na+)

• Anions and cations cannot pass through the lipid bilayer – they must pass through selective channels

Action Potential

• Voltage-gated ion channels– Ions move according to gradient and charge

attraction• Potassium (more permeable)

• Sodium (less permeable)

• Sodium/potassium pump– Requires ATP– Pumps Na+ out of cell and K+ into cell

Action Potential

Myelin sheath

Saltatory Conduction

Other Cells of the Nervous System

• Support

• Nourishment

• Protection

Neuroglial Cells

• Non-neuron cells found in the nervous system– Schwann – forms myelin sheath in PNS– Microglial – protect against microbes– Astrocytes – structural and nutritive support– Oligodendroglial – forms myelin sheath in CNS– Ependymal – line CNS cavities and produce

cerebrospinal fluid

Three Neuroglial Cell Types

Nerve structure

• Bundles of myelin covered nerve fibers (axons) covered in connective tissue

• Blood vessels

Organization• Central nervous system (CNS)

– Brain– Spinal chord

• Peripheral nervous system (PNS)– Motor neurons– Sensory neurons

Path of Impulses

Central Nervous System

• Brain

• Spinal chord

Spinal Chord• Function

– Transmits signals from brain and other parts of the body

– Reflex loop– Simple motor functions (walking, running)

• Structure– Gray matter

• Cell bodies of motor neurons

– White matter• Axons of neurons running up and down spinal chord

Spinal Chord Structure

Pain Withdrawal Reflex

Reflex Loop

Hindbrain

• Medulla – autonomic functions– Breathing, heart rate, swallowing, blood

pressure

• Pons – stages of sleep

• Cerebellum – coordinates muscles– Receives info from position and stretch sensors

Midbrain

• Reticular formation– Sensory relays– Sensory filter

Forebrain

• Thalamus– Transmits info to and from limbic system,

senses, cerebrum and cerebellum

• Limbic system– Basic emotions, drives and behaviors

• Cerebral cortex– Thinking and information processing

Cerebrum

• Two hemispheres– Connected by corpus callosum (white matter)

• Each half divided into 4 lobes– Frontal, parietal, temporal, occipital lobes

• Cortex– 3mm layer of gray matter– Extensive folds to increase surface area

Cerebrum -- Gross Anatomy

• Frontal– Voluntary motor functions, planning, mood, smell

and social judgement

• Parietal– Sensory reception & integration of sensory

information

• Occipital– Visual center of brain

• Temporal– Hearing, smell, learning, memory and emotional

behavior

Functions of Cerebrum Lobes

Sensory Homunculus

• Demonstrates that the area of the cortex dedicated to the sensations of various body parts is proportional to how sensitive that part of the body is.

Sensory Association Areas

• Association areas interpret sensory information• Somesthetic association area (parietal lobe)

– Position of limbs, location of touch or pain, and shape, weight & texture of an object

• Visual association area (occipital lobe)– Identify the things we see– Faces are recognized in temporal lobe

• Auditory association area (temporal lobe)– Remember the name of a piece of music or identify a

person by his voice

Motor Control

• Intention to contract a muscle begins in motor association (premotor) area of frontal lobes

• Precentral gyrus (primary motor area) processes that order by sending signals to the spinal cord

• Motor homunculus is proportional to number of muscle motor units in a region (fine control)

Language• Includes reading, writing, speaking &

understanding words• Wernicke’s area

– Permits recognition of spoken & written language & creates plan of speech

– Angular gyrus processes text into a form we can speak

• Broca’s area– Generates motor program for larynx, tongue, cheeks &

lips – Transmits that to primary motor cortex for action

Language Centers

Aphasia• Any language deficit resulting from lesions in

same hemisphere as Wernicke’s & Broca’s areas• Lesion to Broca’s = nonfluent aphasia

– slow speech, difficulty in choosing words– entire vocabulary may be 2 to 3 words

• Lesion to Wernicke’s = fluent aphasia– speech normal & excessive, but makes little sense

• Anomic aphasia = speech & understanding are normal but text & pictures make no sense

• Others = understanding only 1st half of words or writing only consonants

Lateralization of Cerebral Functions

Cerebral Lateralization• Left hemisphere is categorical hemisphere

– specialized for spoken & written language, sequential & analytical reasoning (math & science), analyze data in linear way

• Right hemisphere is representational hemisphere– perceives information more holistically, perception of spatial

relationships, pattern, comparison of special senses, imagination & insight, music and artistic skill

• Highly correlated with handedness – 91% of people right-handed with left side is categorical

• Lateralization develops with age• Trauma more problems in males since females have more

communication between hemisphere (corpus callosum is thicker posteriorly)

EEG and Brain Waves

• Electroencephalogram records voltage changes from postsynaptic potentials in cerebral cortex

• Differences in amplitude & frequency distinguish 4 types of brain waves

Brain Waves & Sleep• States of consciousness can be correlated with EEG

• 4 types of brain waves– Alpha occur when awake & resting with eyes closed– Beta occur with eyes open performing mental tasks– Theta occur during sleep or emotional stress– Delta occur during deep sleep

• Sleep is temporary state of unconsciousness– Coma is state of unconsciousness with no possible

arousal

Stages of Sleep• Non-REM sleep occurs in stages

– 4 stages occurring in first 30 to 45 minutes of sleep• stage 1 is drifting sensation (would claim was not sleeping)

• stage 2 still easily aroused

• stage 3 vital signs change -- BP, pulse & breathing rates drop– reached in 20 minutes

• stage 4 is deep sleep -- difficult to arouse

– seems to have a restorative effect

• REM sleep occurs about 5 times a night– rapid eye movements under the eyelids, vital signs increase,

EEG resembles awake person dreams

– may help sort & strengthen information from memory

Sleep Stages and Brain Waves

• Brain waves change as we pass through 4 stages of sleep: alpha, to sleep spindles, to theta and finally to delta waves during deep sleep

Cognition

• Cognition is mental processes such as awareness, perception, thinking, knowledge & memory– 75% of brain is association areas where integration of

sensory & motor information occurs

• Examples of effects of brain lesions– temporal lobe -- inability to recognize objects or inability

to recognize faces– frontal lobe -- problems with personality

Memory• Information management requires learning,

memory & forgetting (eliminating the trivia)– Abnormalities

• pathological inability to forget have trouble with reading comprehension

• can not store new data• can not remember old data

• Hippocampus - organizes sensory & cognitive information into a memory– lesions cause inability to form new memories

• Cerebellum helps learn motor skills• Amygdala important in emotional memory

Emotion

• Prefrontal cortex controls how emotions are expressed (seat of judgement)

• Emotions form in hypothalamus & amygdala– artificial stimulation produces fear, anger, pleasure,

love, parental affection, etc.– electrode in median forebrain bundle in rat or human

and a foot pedal• press all day to the exclusion of food (report a quiet,

relaxed feeling)

• Much of our behavior is learned by rewards and punishments or responses of others to them

Peripheral Nervous System

• Motor neurons

• Sensory neurons

Organization of Nervous System

Motor Neurons

• Carry signals from the CNS to muscles and glands– Somatic – voluntary responses

• Skeletal muscles

– Autonomic – involuntary responses• Cell bodies found in ganglia

– Organs

– Glands

– Smooth muscles

Sensory Neurons

• Mechanoreceptor– Hearing, pressure, stretch, movement

• Photoreceptor– Light, vision

• Chemoreceptor– Olfactory– Taste– Pain

Sensory Receptors

• Where is the stimulus located?

• How strong is the stimulus?

• Stimulus = energy

• Sensory receptors transfer signal to other neurons

• Specialized cells or modified neurons

Receiving Sensory Information

• Sensory Transduction– Converts received signal to action potential

• Amplification– Signal transmitted contains more energy than

signal received

• Transmission– Action potential

• Integration– Information processing

Types of Sensory Receptors• Mechanoreceptor

– Stretch or bending of plasma membrane• Hearing, pressure, stretch, movement

• Chemoreceptor– Binding of specific molecules to protein receptors in

plasma membrane• Olfactory, taste, pain

• Photoreceptor– Photons hitting specific proteins in plasma membrane

• Vision

Touch

• Mechanoreceptor

Parts of the Ear

• Outer ear– Pinna and auditory canal

• Middle ear– Tympanic membrane (ear drum)– Ossicles (malleus, incus, stapes)

• Inner ear– Cochlea

Auditory Receptors• Different pitches vibrate different

parts of the basilar membrane

• The basilar membrane vibrates against hair cells in the cochlear duct

• Shape and thickness of basilar membrane effects vibrations

Pain Receptors

• Chemical receptor– Detects chemicals

released during tissue damage

– Receives chemical on specialized dentrites

Olfactory Receptors

• Chemical receptor

• Different molecules have different cells with unique receptors for that molecule

Photoreceptors• Modified neurons containing light

absorbing pigment

• Rods– Black and white– Night vision– Pigment – rhodopsin

• Cones– Color– 4 types – red, blue and green– Pigment – photopsins

Photoreceptor Function

• Photoreceptor constantly firing in dark which inhibits post synaptic neuron

• Light releases inhibition of postsynaptic neuron

Retinal Structure

• Rods and cones are not mapped 1:1 to ganglion cells

• More cells per ganglion cell equals lower resolution but greater sensitivity

• Dogs have 5x the number of rod cells per ganglion cell

• Optic nerve exits through the fovea which creates your blind spot