Nervous system. Nervous system. Nervous system. Nervous system. Nervous system: Neuroglial Cells. Nerve tissue cells CNS CNS

Nervous system Words to know: general Nervous system • CNS: Central Nervous system= the brain and spinal cord • PNS: Peripheral Nervous system= “ever...
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Nervous system Words to know: general

Nervous system • CNS: Central Nervous system= the brain and spinal cord • PNS: Peripheral Nervous system= “everything else” • Afferent: signal travels “towards”

Sensory

• Efferent: signal travels “away from”

Motor

•Somatic: “of the body” think of this as “voluntary” • Autonomic: “automatic” think of this as “involuntary”

Nervous system

Nervous system

More words to know: Autonomic system

CNS

• Sympathetic: “fight or flight” - What changes would you expect in the body when needing to fight or flee?

afferent

efferent

• Parasympathetic: “rest and digest” •- what changes are expected in a “feeding” or resting mode? Sensory

motor

Peripheral Nervous System

Nerve tissue cells • Cells are tightly packed (compared to other tissues) • Neurons • “everything else”– Neuroglial cells

Nervous system: Neuroglial Cells •CNS Astrocytes- star shaped. •Most numerous of glial cells •Support neurons, linking to surrounding tissues •Direct neuron growth direction and attachment (synapse formation •Recycle neurotransmitters •maintaining the blood brain barrier- a wrapping around capillaries in the brain, affecting capillary permeability

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Nervous system: Neuroglial Cells

Nervous system: Neuroglial Cells •CNS

•CNS •Microglia- nervous system “cootie catchers”. •Surveyors of damaged cells and infectious agents. •These become functional macrophages

Nervous system: Neuroglial Cells •CNS

•Ependymal cells •Line the cavities (ventricles and spinal column) of the brain •SquamousÆcolumnar •Some ciliated •Help form and circulate the cerebrospinal fluid

Nervous system: Neuroglial Cells •PNS

•Oligodendrocytes : myelin producing cells •Cell extensions wrap nerve fibers in a myelin sheath

•Schwann Cells : myelin producing cells •Cell extensions wrap nerve fibers in a myelin sheath •Help to regenerate damaged neurons •Satellite cells: Function?

Nervous system: Cells of the nervous system Neurons -sensory -motor -interneurons

Neuroglia

Cells

Neurons Essential function is to transmit signals

-Astrocytes -Microglia -Myelin producers -Oligodendrocytes -Schwann - Satellite cells

Can live a long time (essentially a life-time) Generally do not divide Dependent on aerobic metabolism (so very vulnerable to loss of oxygen)

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Nervous system:

Cells

Words to know- Neurons Cell Body (aka perikaryon, soma)- in the CNS or ganglia -the nucleus and most of the cytoplasm are here

Nervous system:

Cells

Words to know- Neurons Dendrites- carry afferent signals. Carry signals towards the cell body. Several of these (“hundreds” in a motor neuron) in a multipolar neuron

-Generally lacks centrioles (which would be involved in cell division) -Lots of rough ER and ribosomes (stain dark, therefore “chromatophilic substance”) -Can accumulate a pigment “lipofuscin”– associated with older cells and lysosomal activity

Nervous system:

Cells

Words to know- Neurons Axon- carry efferent signals. • Carry signals away from the cell body. •One of these in any neuron •Arises from the axon hillock of the cell body •May be quite long or very short •The long axons are called “nerve fibers”

Nervous system:

Cells

Words to know- Neurons Axon-(cont) •Axons can branch, with many “terminal branches” (“10,000 or more”) – those at the end furthest from the cell body •The ends of these branches (as seen at the neuromuscular junction) are called “axon terminals” or “synaptic knobs” or “boutons” •The ends are the source of the released neurotransmitter

Nervous system:

Cells

Words to know- Neurons

Nervous system:

Cells

Neurons: Carrying electrical signal- the communicators Dendrites- carry afferent signals. Carry signals towards the cell body. Several of these in a multipolar neuron

Dendrites

Cell Body- where lies the nucleus and most of the cytoplasm

Cell body

Axon- carry efferent signals. Carry signals away from the cell body. One of these in any neuron Myelin- an insulating covering of many (not all) axons. Myelin speeds the rate of signal conduction along an axon.

Axon Nodes

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Nervous system:

Myelin

There are 2 types of myelin producing cells. •Oligodendrocytes -located in the central nervous system

Nervous system:

nerves and neurons

•As with the muscular system, there is a challenge with language. When we say “nerve” we may be speaking of a single neuron or a named “cable” of nerve axons.

•Schwann cells - located in the peripheral nervous system.

Examples: median nerve (arm/wrist), sciatic nerve

•In both cases, Myelin covers axons and speeds nerve signal.

•Nerves are also wrapped in layers of fascia, and bundled within the “cable”, as muscle cells are within the larger muscle.

Potential

Potential

“Potential” is a “difference” In reference to a nerve membrane, “potential” is maintained by positive and negative charges unevenly distributed between the inside and outside of the neuron. A disturbance of the cell membrane alters its permeability to charged particles---allowing them to move through the membrane--- and thus changes the “potential” ++++ - - - -

Nervous system:

nerves and neurons words to know Potential

•Potential: “something could happen here”. Describes a difference between 2 things. In the body, refers to an electrical charge difference on 2 sides of a cell membrane •depolarization: the difference between 2 sides or regions has become less.

Nerve signal conductiona wave of depolarization Because of the difference in positive and negative ions outside and inside the nerve, we say that them membrane is polarized. The amount of “difference” (potential) between inside and outside is the same as the degree of polarization

See pages 397 of text

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Nervous system:

nerves and neurons --how nerves work---

Nervous system:

nerves and neurons --how nerves work--The electrical potential is due to mineral ions and proteins with charges, distributed unevenly to the inside and outside of the cell.

See pages 399 of text

Some definitions • Voltage- measure of potential energy (because of the separation of charges)More difference between 2 points = higher voltage= greater potential energy

Some definitions • Current – flow of electrical charge– gets used to “do work” • - depends on voltage (how “steep”) and resistance (how much is in the way)

– A “steeper hill”

Some definitions • Resistance: getting in the way of flow – Something that does this well is an insulator – Something that doesn’t resist and allows flow is a “conductor”

Some definitions • The law (Ohm’s) says Current= Voltage/resistance.

Or, “if the hill is steeper, the water flows more, unless there’s more stuff in the way”

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Some definitions Note- in electrical systems like light bulbs, the electrical current is generated by flowing electrons. In living systems (and so “nerves”), we’re talking about ions, not free electrons.

Ion flow • For ions to flow through a membrane, there must be a way through. • - some channels “leak” • The Na/K pump helps “bail” the leakage • - others open to particular conditions • “ligand”, “voltage” “mechanical” • See 398

Resting Potential • -70 mv (-40 to -90, depending on neuron) • This is the nerve “at rest” • (see 399)

More definitions • Depolarization: – The difference across the membrane decreases, and approaches “0” • It may actually switch– that is, instead of being “less negative”, it actually becomes slightly positive inside relative to the outside. This is still called “depolarization”

More definitions

More definitions

• Hyperpolarization: – The difference across the membrane increases, that is becomes “more negative” inside.

• Graded potential: -depolarization changes on part of the membrane. The degree of change and the distance along the membrane depends on the strength of the stimulus - a signal is carried, but not very far

• The result is that it takes a stronger stimulus to get an action potential going

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More definitions • Action potential: -depolarization along the whole length of the axon - requires a certain minimal (threshold) stimulus - essentially the same as the action potential in muscle

Action Potential 1. Na channels open due to the initial stimulus, then continue opening d/t polarity changes (Na rushes in) 2. Na channels close, K channels open. (K moves out) 3. Na/K pump restores chemical gradient

Action Potential An “All or none” event: either the signal strength was strong enough to reach threshold or not. If the signal was strong enough, the “chain reaction” happens

Action Potential Refractory period: “absolute”- the nerve cannot be stimulated. This is due to Na channel closure– allows them to “reset” “relative” a stronger stimulus is needed than would be at rest. Some channels have reset. Not all. Repolarization is still occurring

Nervous system:

nerves and neurons --how nerves work---

Action potential • Larger axons conduct the signal faster

The nerve signal is carried as a • Myelinated axons conduct the signal faster

wave of depolarization along the nerve membrane

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Nervous system:

nerves and neurons --how nerves work---

Synapses • Connections can be axon-body or axondendrite. • A presynaptic neuron carries a signal to a postsynaptic neuron.

Saltatory conduction in a myelinated axon

The signal from one nerve to another (or to another cell type) can be excitatory or inhibitory. The effect on the target is determined by the total of all the signals.

When the wave of depolarization reaches the synaptic knob, Ca channels open. The influx of Ca causes the release of a neurotransmitter .

1) When the wave of depolarization reaches the synaptic knob, Ca channels open. The influx of Ca causes the release of a neurotransmitter . 2) The neurotransmitter binds to the post-synaptic membrane, causing the opening of ion channels. (and results in depolarization of the target)

Nervous system:

nerves and neurons --how nerves work--Neurotransmitters Serotonin Acetylcholine Dopamine Norepinephrine

3) Neurotransmitter is removed …

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Neurotransmitters Acetylcholine(Ach), Norepinephrine (NE) dopamine, serotonin, others

Once released, the neurotransmitter diffuses across the synaptic cleft and binds to receptors to have its effect. Enzymes near the receptors quickly break down the neurotransmitter, limiting the effect.

The effect of a neurotransmitter binding can be stimulating or inhibiting. The effect depends on the neurotransmitter and the type of receptor. See table 11.3

Brain and Spinal Cord

Brain and Spinal Cord

The spinal cord and brain are really both portions of a long tube formed during embryonic development.

Superiorly, the tube grows, elongates, becomes the structures of the brain.

This tube enlarged and folded at one end to form the brain.

The center opening of the tubes becomes the ventricles of the brain and the central cavity of the spinal cord

From both brain and spinal cord, pairs of nerves “branch off” towards other regions of the body, carrying sensory and motor information.

CSF (Cerebral spinal fluid) circulates through the ventricles, central cavity and outside brain and spinal cord in the arachnoid space.

Cerebrum: handles memory, conscious thinking, voluntary motor Diencephalon: includes the thalamus, hypothalamus, pituitary Midbrain: between pons and diencephalon- in addition to fibers passing through, there are nuclei dealing with sight and hearing. Pons: Connects there cerebellum into the brain stem. Also some cranial nerves arise here Medulla:Connects brain and spinal cord; more cranial nerves; some important autonomic controls

Cerebrum: voluntary and conscious processing :has a gray matter cortex about 1/8th inch thick :has gray matter buried deeper inside- the basal nuclei

:has lots of white matter

Words to know: lobe, sulcus, gyrus, fissure

Cerebellum: “Compares the higher brain’s intent with what the body actually did”. Maintains posture.

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Gyrus: increases surface area

Lobes

Sulcus: grooves or spaces between gyri Longitudinal fissure: divides hemispheres– is deep , going al the way to the corpus callosum. Falx cerebri runs here Lobes: Frontal lobe anterior to central sulcus : temporal- inferior to lateral sulcus

• • • • •

Frontal Parietal Temporal Occipital Insula (deep to lateral sulcus)

: parietal- between central and parieto-occipital sulcus :occipital- posterior to parieto-occipital sulcus :insula- a 5th lobe, buried under the temporal

Cerebral Cortex • Outer grey matter of cerebrum • Made up of interneurons • Functionally divided into sensory, motor, association areas • Mostly sensory and motor functions relate to opposite side of the body • Structure is symmetrical. Functions are distributed between sides (specialization)

Cerebral Cortex- sensory

Cerebral Cortex- motor • Primary Motor- precise intentional movements for opposite side- precentral gyrus • Premotor cortex- learned/patterned actions anterior to precentral • Broca’s area- speech planning and other voluntary motor- anterolateral (one side only?) • Frontal eye field- voluntary eye movementsanterior

Cerebral Cortex- sensory

• Primary Somatosensory-ID’s regions of body stimulated- postcentral

• Olfactory cortex- awareness of odorsmedial cortex

• Somatosensory association cortex- takes raw sensory data and interprets or recognizes

• Gustatory cortex- taste-- insula

• Visual area and visual association- takes data from retina, interprets; occipital

• Visceral sensory- stomach ache, full bladder ,etc-- insula

• Auditory and association- raw sensation and interpretation- temporal lobe at lateral sulcus

• Vestibular cortex-equilibrium-- insula

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Cerebral Cortex “multimodal association” • Anterior assoc.- intellect, planning, abstraction, judgment

Association areas: parts of the brain that help bring sensory information to consciousness/ realize motor intents

• Posterior assoc.- pattern and face recognition, finding context for events • Limbic assoc.- emotional interpretation See p. 441

Lateralization • Functions distributed to different hemispheres. • -Right brain- vs. Left brain

Early in development, the brain goes through a “lateralization” where one hemisphere becomes “dominant”, giving rise to the notion of “right brain” or “left brain”

It is suggested that failure of this lateralization can result in learning difficulties. (Marieb text)

• See 441

Cerebral white matter

Basal Nuclei: Grey matter concentrations within the white matter of the cerebrum

• Remember white matter is myelinated fibers – Commisures:- connect opposite grey matter areas between hemispheres – Association fibers- connect within a hemisphere – Projection- run between levels (upper/lower– brain/spinal cord)

Caudate nucleus Lentiform nucleus Globus pallidus Putamen see 444

Collectively, are involved in smoothing out muscle movements/coordinating movement (simplified version)

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Diencephalon Epithalamus: link with the pineal gland, melatonin and circadian cycle Thalamus: relay and rough sorting of information

Hypothalamus: “old brain” autonomic functions

Diencephalon Hypothalamus: “old brain” autonomic functions -basic emotion - ANS control -temperature control -hunger, thirst -sleep/wake - major control of pituitary function

Diencephalon Thalamus: - either side of the 3rd ventricle, connected by the “intermediate mass”/”interthalamic adhesion” -contains many smaller nuclei with particular specialties, related to particular areas of the cortex -relay and rough sorting of sensory information from other regions (lower body and hypothalamus)

Diencephalon Epithalamus: link with the pineal gland, melatonin and circadian (sleep/wake) cycle

see details 446

Brain stem

Midbrain- contains cerebral aqueduct, connecting 3rd and 4th ventricles -nuclei for cranial nerves (3,4) and visual/auditory reflexes

Brain stem

Pons-a link between spinal cord, cerebellum and higher brain -Nuclei for cranial nerves 6,7

- “substantia nigra” neuron loss related to Parkinsons

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Cerebellum

Brain stem

Medulla- Important autonomic nuclei here - cardiovascular, respiratory centers, others (451) - More cranial nerve nuclei here

Functional systems • Activities of neurons in the brain crossing between several regions to complete a particular type of task – Limbic system- emotions/feelings

• Coordinates between the motor cortex, sensory input, brain stem nuclei to allow correct sequencing of movements. • Unconscious functioning • Has its own cortex and white matter- forming “arbor vitae” pattern • “Compares the higher brain’s intent with what the body actually did”

Functional

systems

• Limbic system– Parts include • • • • •

the cingulate gyrus (medial hemisphere) Amygdala- part of basal nuclei- see 444, 455 Hypothalamus*** Nuclei in thalamus Interaction w/ prefrontal lobes

– Reticular formation-filter of sensory input, alertness

Functional

systems

Reticular formationparts include nuclei in themedulla pons midbrain and connections broadly through the cerebrum

Brain waves • Electrodes attached to the scalp can measure electrical activity patterns from neurons in the cortex. • Wave patterns of this electrical activity can be useful diagnostically (see 457)

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Brain protection • • • •

CSF Meninges Skull Blood- brain Barrier

Ventricles- cavities in the brain containing cerebral spinal fluid

2 lateral ventricles are indirectly connected to the 3rd ventricle which connects via the cerebral aqueduct to the 4th ventricle in the pons and superior medula

CSF: supports/cushions the brain carries nutrients and wastes total volume 150 mls (1 tsp=5 mls)

Blood Brain Barrier

Spinal Cord

• Fluid gets in going through the capillary wall, (the thicker basement membrane of the capillary) and the additional wrapping of the astrocytes . – Selects for glucose, particular amino acids – Selects against some other molecules – Doesn’t protect against lipid soluble substance

Nervous system:

Spinal cord

Nervous system:

Spinal cord

words to know: • From Brain to Lumbar spine • 31 pairs of spinal nerves

Spinal nerve: one of 31 pairs of nerves coming out of spinal cord

• Lower end “frayed” into cauda equina (horses tail)

Gray Matter: unmyelinated regions of spinal cord (and brain)

• Contains regions of myelinated nerves (axons) and unmyelinated nerves (dendrites and cell bodies)

White Matter: myelinated regions of spinal cord (and brain) Ganglion: a group of cell bodies located outside the CNS

• Contains fairly discrete regions that are groups of fibers carrying specific signal types (pain, temperature, touch…, voluntary motor)

Root: the ventral or dorsal division of a spinal nerve Tract: bundle of nerve fibers carrying a particular type of nerve signal

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Nervous system:

Spinal cord

Nervous system: Spinal cord

words to know: Ventral Horn- neurons related to voluntary movement Dorsal Horn- interneurons related to sensory neurons (sensory neuron body’s in the dorsal root ganglion) Lateral Horn- autonomic motor neurons (to viscera) Columns: a groups of fibers in the spinal cord. Bundles of myelinated axons (=funiculi)

See p. 473

Nervous system:

Spinal cord

White matter: myelinated and unmyelinated axons Gray matter: cell bodies and glial cells

Dorsal root sensory

Dorsal root ganglioncontains cell bodies of sensory neurons

Compare to the brain– Motor tends to be anterior/ventral sensory tends to be dorsal/posterior

Mixed nerve Ventral root motor See text p. 473

Nervous system:

Spinal cord

Dermatomes:

Don’t panic: get that there are specific regions of the lateral white columns carrying specific kinds of information Ex: spinothalamic tract carries touch, pressure, pain, temperature in corticospinal carries voluntary muscle out See Text p. 475

See text p. 518

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Nervous system:

Spinal cord

Dermatomes:

Each sensory nerve leaving the spinal cord provides sensory innervation to a particular region of the skin. This innervation is in a regular pattern and can be mapped as “dermatomes”

Some part of most individual spinal nerves is responsible for the innervation of a particular region of skin. The region each spinal nerve innervates is fairly consistent between individuals. This fact can be useful diagnostically The region of skin innervated by a particular spinal nerve is called a Dermatome.

Reflexes • Components – Receptor – Sensory Neuron – CNS integration site • (may be direct contact between sensory and motor. May be more involved)

– Motor neuron – Effector (muscle or gland)

Reflexes • Identified reflexes – Stretch and Golgi tendon Organ • Proprioceptive feedback on muscle length and tension

– Flexor and Crossed extensor (526) – Superficial • Plantar • Abdominal

– Pupillary light and consensual, accommodation

Reflexes-visceral • Similar to somatic reflexes: (542) – – – – –

Stimulus (chemical, stretch, irritation) Sensory receptor Some kind of “integration” Motor neuron Effector

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