the nervous system neurons and synapses

two types of cells

neurons and neuroglial cells

what are neurons

transmit electrical signals, found in grey matter of CNS and ganglia

• basic structural unit of nervous system

• possess a cell body and processes called neurites

• human body contains billions of these

what are neuroglia cells

support cells; non-excitable, surround and wrap neurons

characteristics of neurons

• conduct electrical impulses along plasma membrane

• produce nerve impulse and action potential

• can live and function for a lifetime

• don’t divide; fetal neurons lose ability to undergo mitosis

• high metabolic rate; needs lots of oxygen and glucose

types of neurons

unipolar, bipolar, multipolar

axons of neurons are covered by what

myelin sheaths which has nodes of ranvier that accelerates action potential

myelinated axons makes what faster

action potential (AP)

cell body has…

nucleus, dendrites, axon, and end terminals

the internal environment of the ganglion supports synapses between what fibers

pre and postsynaptic fibers

4 types of glial cells in CNS

• oligodendrocytes

  • same as schwann but for CNS

  • form myelin sheaths around axons of CNS

• mircoglia cells

  • not active until there is an infection

  • migrate through CNS and phagocytose foreign and degenerated material

• astrocytes

  • regulate external environment of neurons in CNS

• ependymal cells

  • line the ventricles of brain and central canal of spinal cord

  • helps accelerate CSF

two types of supporting cells in PNS

• schwann cells

  • form myelin sheaths around peripheral axons

• satellite cells (ganglionic gliocytes)

  • support neuron cell bodies within the ganglia of PNS

function of astrocytes

• cell proliferation occupy gap area in brain which controls glutamate, GABA concentration and potassium concentration in CNS

• helps in formation of blood brain barrier

• absorbs glucose from capillaries

• absorb excess K+ of extracellular fluid

• phagocytosis of degenerated axon terminals

• prevent regeneration process

function of ependyma cells

lines central cavities of brain and spinal cord; has microvilli also

function of oligodendrocytes

• myelination in CNS

• can also influence the biochemical environment of neurons

function of microglia

• in normal CNS → inactive

• in inflammation/degeneration of CNS → proliferate and become active and phagocytic

gliosis and glial scar

• hyperplasia and hypertrophy of astrocytes that occur in reaction to CNS injury

• oligodendrocytes respond to injury by expanding and vacuolation of their cytoplasm

tumors of neuroglia (glioma)

• accounts for 50% of intracranial tumors

• astrocytomas and glioblastomas are tumors of astrocytes

• apart from ependymomas, they are very invasive and grow large with minimal effect on neighboring neurons

multiple sclerosis (MS)

• demyelinating diseases of CNS

• neurodegenerative disease

• unknown disease

• occurs between 20-40 yr olds

• usually starts with optic nerve, spinal cord, and cerebellum

• axonal degeneration b/c of demyelination and/or early in the course of the disease is part of the disability

• affects sensory and motor disorders

if multiple sclerosis (MS) involves the diaphragm muscle, what will happen

respiration is blocked, which can cause death

neurotrophins

• in developing fetal brain, chemicals called neurotropins help with neuron growth

  • nerve growth factor (NGF)

  • brain-derived neurotropic factor (BDNF)

  • glial-derived neurotropic factor (GDNF)

  • neurotropin-3

    • important in embryonic development of sensory neurons and sympathetic ganglia

blood brain barrier (BBB)

• border between brain tissue and capillaries formed from tight junctions, endothelial cells, and basement membrane

• prevents passage of large sized molecules into brain tissue

  • O2, CO2, H2O, alcohol, small sized proteins, drugs, cocaine, and marijuana can enter

• dopamine can’t pass through BBB but L dopa (precursor) can which can develop into dopamine to help treat parkinson’s disease

function of BBB

• maintain constant environment for neurons in CNS and protects the brain from endogenous or exogenous toxins

• prevents the escape of neurotransmitters from their functional sites in CNS into the general circulation

• drugs penetrate BBB to varying degrees such that nonionized can cross more readily than ionized drugs

  • inflammation, irradiation and tumors may destroy BBB and permit entry into brain of substances that are usually excluded

both CSF and blood have what; CSF = blood

• Na+

• Cl-

• HCO3-

• osmolarity

CSF has less of what than blood; CSF<blood

• K+

• Ca2+

• glucose

• cholesterol

• protein

CSF has more of what than blood; CSF>blood

• Mg2+

• creatinine

neurotransmitters

acetylcholine (ACh), norepinephrine, epinephrine, dopamine, glycrine, serotonin, gamma-amiobutyric acid (GABA), enkephalines, substance P, and glutamic acid

Ach

found at NMJ, in automatic ganglia, parasympathetic nerve

norepinephrine

found at sympathetic nerve endings, in CNS: in hypothalamus

glycine

found in synapses in spinal cord

glutamate

excitatory amino acid neurotransmitter in many central nervous neurons

treatment of certain neurological diseases by neurotransmitters

• parkinson could be treated to some extent by neurotransmitters

  • dopamine can’t cross BBB, but its precursor L-dopa can

• synaptic blocking agents

deficiency in acetylcholine leads to what

muscle weakness

excessive ACh leads to what

muscle spasms and diarrhea and gastritis

clinical significance of norepinephrine (NE)

• to alpha-1: constriction

• to alpha-2: relaxation

• to beta-1: increase heart rate and conduction velocity

• to beta-2: relaxation of bonchi

• also causes hypertension

dopamine clinical significance

• deficiency → parkinson’s

• excessive → schizophrenia

• deficiency in hypothalamus → hyperprolactemia

• deficiency in frontal lobe → social behavior disorders

glutamate is for

memory and learning

deficiency of serotonin causes

• depression

• bipolar disorder

• migraine

• increase aggression and angry behavior

regulatory molecules are

• epinephrine

• norepinephrine

• dopamine

• serotonin

serotonin

• in CNS, plays role of regulation of anger, aggression, body temp., mood, sleep, vomiting, sexuality, and appetite

dopamine

• produced in several places

  • substantia nigra

  • hypothalamus

• function as a hormone → inhibit release of prolactin from anterior lobe of pituitary

• can be used as medication

norepinephrine

• released from adrenal medulla of adrenal glands as a hormone

• as a stress hormone → affects parts of human brain where attention and responding actions are controlled

• underlies fight or flight response, directly inc. heart rate, triggering release of glucose from energy stores, and inc. skeletal muscle readiness

most common inhibitory neurotransmitters

GABA and glycine

neuropeptide Y is for

appetite and satiety (feeling of being full from eating)

nitric oxide as a neurotransmitter

relaxation of blood vessels and erections in males

CLINICAL CASE:
50yr old male has head trauma w/ severe headaches, vertigo, can’t see well in right eye, vomiting, coughing, palpitation, confusion, and speech disorders. which part of CNS have been damaged?

damage to

• left area with broca’s area

• right optic nerve

• hypothalamus

• vestibular system

• medulla oblongata (coughing)

CLINICAL CASE:

patient has severe abdominal pain, diarrhea, palpitations, hypertension, nose bleeding, headaches. what is the cause

excess ACh and norepinephrine

CLINICAL CASE:

65 yr old male has depression, sleep disorders, lack of appetite, mood disorders, erectile dysfunction, infertility. what is the cause

deficiency of serotonin, dopamine