KU SPLH 620

Nervous system

The nervous system has a network of neurons and controls body functions, receives input, transmits information, integrates input, generates commands and outputs to motor systems.

Location of the CNS

Brain and Spinal Cord

PNS (peripheral nervous system)

Somatic and autonomic, which both branch to afferent and efferent nerves.

Anterior vs. Posterior

Anterior (front), posterior (back)

Superior vs Inferior

Superior (above)

Inferior: (below)

Medial vs lateral

Medial is toward midline, lateral is away from midline

Ipsilateral vs contralateral

ipsilateral: same side

contralateral: opposite side

Afferent vs efferent

afferent (sensory and arriving to brain) and efferent (motor and exiting brain)

Sagittal plane

Divides body into right and left planes

Coronal/frontal

Divides the body into anterior and posterior plane

Axial/transverse

Divides the brain structure into upper and lower

Neuroglia

Provides physical support, nutrient flow and nerve housekeeping

Cell types in NS

Neurons (information carriers) and Glia (support cells)

What do astrocytes (CNS) do

Provide nutrients, regulate external cellular fluid, clean up debris

What does microglia do (CNS)

Immune cells, smallest glial cells, protect brain from invading microorganisms

What does oligodendroglia do (CNS)

CNS myelination cells, extend processes to multiple axons sections, produce myelin sheath

What do schwann cells do (PNS)

PNS myelination cells, single myelin section, support cells

Why is myelination important?

Myelin is made of lipid and protein and acts as an insulator during conduction of electrical impulses through nerves surrounding the axon, and increases the speed at which impulse travels

What happens when you lose myelination?

Nerve impulses slow down or stop

Neurons

Information processing and transmitting element in the NS, there is 100 to 100 billion in NS

Parts of the cell body and what they do

1. Cell body: integrates signals

2. Dendrites: receives signals

3. Axon: conduit to send signals

Electrical neuron signaling

Information flow through neurons. Dendrites collect electrical signals, cell body integrates incoming signals and generates outgoing signal to axon, axon passes electrical signal to dendrites of cell.

Chemical neuron signaling

Synapse: presynaptic neuron, synaptic cleft and postsynaptic neuron.

What happens in presynaptic and postsynaptic neurons

Presynaptic is axon terminal where neurotransmitters are released, postsynaptic is the dendrite where the neurotransmitter binds.

Action potential

Fundamental unit of neural communication, depolarizing potential, once generated it is propagated down the axon

Neurotransmitters

Acetylcholine, glutamate, GABA, dopamine, norepinephrine, serotonin

Post-synaptic receptors

neurotransmitters diffuse across synaptic cleft and bind to the postsynaptic receptor. Postsynaptic receptors open neurotransmitter dependent ion channels in response to binding, Na+ and K+ channels

Post synaptic potentials

EPSP and IPSP

What charge is depolarization

• positive

Hyper-polarization level

below -70 mV

Iontropic vs metabotropic:

2 recpetos that determine affects on postsynaptic neuron. Iontropic is direct opening of channels due to binding and fast transmission, metabotropic is indirect and slow transmission.

EPSP

EPSP is depolarizing potential, moves cell membrane toward its threshold voltage opening sodium channels making cell more positive. If threshold is reached, AP is generated

IPSP

Opens potassium channels, potassium moves out of postsynaptic cell making cell more negative, cell is inhibited and less excitable.

Spatial summation

Multiple synapses are activated at once, the effects may add up in space.

Temporal summation

A given synapse is activated repeatedly, the affects can add up in time.

Threshold potential

Threshold of excitation is -55 mV

Resting membrane potential

70 mV, the charge inside the cell is 70 mV less than the outside. If RMP moves past threshold, membrane moves to +40 mV then returns to resting

Saltatory conduction

Axons originate at axon hillock, they are propagated down axon and depolarize each successive patch of membrane. Myelinated axons- fast transmission. Unmyelinated axons= slow transmission. AP jumps from node to node only depolarizing membrane at node.

Excocytosis

process of releasing synaptic vesicles. AP propagates down axon terminal, voltage change allows for entry of CA++ ions and triggers exocytosis. It occurs where vesicles fuse with membrane. NT diffuses across cleft to interact with PS membrane.

Reuptake

termination that keeps PSP short, presynaptic uptake and recycles the transmitter

Sensory receptors

specialized cells housed by sensory receptor organs to detect specific stimuli

Characteristics of encoding stimulus

type, intensity, duration, location

How are stimuli encoded

Produce electrical signals that represent all 4 aspects of stimuli. They encode some aspect of the external or internal environment into a graded electrical signal (receptor potential)

Types of sensory receptors/modalities

Chemoreceptor, thermoreceptor, photoreceptor, mechanoreceptor, nociceptor

Receptor potential

Graded potentials that reflect stimulus, not propagated actively, so receptors that signal over long distances must generate APs

Encoding intensity and duration

More intense stimuli produce larger receptor potentials and longer stimuli cause longer receptor potentials- encoding intensity and duration of stimulus. Can be slow or fast transmission depending on receptor type. Logarithmic relationship

What is transmission velocity dependent on?

Receptor type

Difference between receptor potential and action potential

When a receptor receives a stimulus, it begins to fire action potentials at an increased frequency

How to process intensity?

Different sensory receptors adapt to maintained stimuli at different times

How to get a dynamic range?

Combining receptors with different sensitivity gives dynamic range and high sensitivity to change

Receptive field

area on the body or sensory space where a stimulus can activate the receptor

Adapting rate

Slowly adapting receptors produce a maintained response to a constant stimulus. Rapidly adapting receptors response declines and may disappear entirely during a constant stimulus.

Somatosensation modalities

Discriminative touch, pain and temperature, and proprioception

Mechanoreceptor

Activated by mechanical displacement, discriminative touch

Proprioceptors

Muscle spindle receptors, golgi tendon organs, joint capsule receptors. Receptors in the skin can also signal postural information. Important for lip movements and facial expression

Thermoreceptors

temperature, activated by changes in temperature

Nocireceptors

Pain, activated by damage to tissue

Morphology

Peripheral process central process, cell body location

DCML pathway

dorsal column---> dorsal column nucleus (x @ medulla) ----> medial lemniscus ----> thalamus ----> primary sensory cortex)

MSTP

(main sensory trigeminal nucleus (x) ----> ventral trigeminal lemniscus ---> thalamus ---> primary sensory cortex)

ALS pathway

(interneurons in spinal cord (x @ ventral white commissure) ---> anterolateral spinal cord/spinothalamic tract ---> thalamus ---> primary sensory cortex)

STP

( spinal trigeminal nucleus (x) ---> ventral trigeminal lemniscus ---> thalamus ---> cerebral cortex)

Where is the primary sensory cortex?

Parietal lobe, in the post central gyrus, anterior part of the lobe

What is somatotopy?

Precise mapping of body parts to specific areas of the brain

Cranial nerves

Most originate in the brainstem, they provide motor and sensory innervation for head and neck

I olfactory

sensory, smell

II optic

sensory, vision

III oculomotor

motor, eye movement

IV trochlear

motor, eye movement

V Trigeminal Nerve

sensory for the face; motor fibers to chewing muscles

VI abducens

motor, eye movement

VII facial

controls most facial expressions

secretion of tears & saliva taste. somatic and visceral, sensory

VIII Vestibulocochlear

sensory, hearing and balance

IX Glossopharyngeal

taste, motor and sensory

X Vagus

taste, sensory and motor

XI Accessory (spinal)

Motor- Muscles of pharynx

XII hypoglossal

motor, tongue movement

Somatic sensory

touch and proprioception and pain and temperature

Visceral sensory

Relating to sensory receptors in visceral structures, taste

Special sensory

Relating to smell, vision, hearing and balance

Motor

Oculomotor, trochlear, abducens, accessory, hypoglossal

Sensory

Somatic, visceral, special

Mixed

Facial, glossopharyngeal, vagus

Brainstem cranial nerve nuclei

10 exit from the brainstem, CN exits dorsally

Sensory nerves involved in speech and/or hearing

Glossopharyngeal: posterior tongue

Trigeminal: anterior tongue and face

Vagus: pharynx and larynx

Vestibulocochlear: hearing

Six stages of sensory processing

Stimuli, transduction, encoding, transmission, translation, integration

What two stages are central processing

Translation and integration

Gray matter

Mostly cell bodies of nerve cells and glial cells and dendrites, unmyelinated axons

White matter

Myelinated axons

Sulci and gyri

Cortical surface in the cerebral cortex is convolved into sulci and gyri to fit more surface area in a given volume. Deep sulci are called fissures

5 cerebral lobes

Frontal, parietal, temporal, occipital, insular

What are the functional cortical areas

Primary motor projections, primary sensory reception, association areas