Nervous Tissue Flashcards
Functions of the Nervous System
Co-ordination
Control
Information
processing
Perception ‘Thinking’
& ‘Feeling’
Emotions Memory
Sensory function
ORGANISATION
Central nervous system (CNS)
Peripheral nervous system (PNS)
THE SPECIALISED CELLS OF
THE NERVOUS SYSTEM
Neurons
- Generate & propagate electrical
signals (action potentials)
Glial cells
-Support and maintenance of the
extracellular environment
- Various types including astrocytes, microglia, oligodendrocytes
and ependymal cells
CELL TYPES- NEURONS
Initiate, propagate and
transmit nerve impulses (action potentials)
- Cell body- contains
nucleus and organelles - Dendrites- carry signals
TOWARDS cell body=
INPUT - Axons- carry signals
AWAY from cell body =
OUTPUT - Axon terminal- structures
specialised for neural
signalling
AXONS
- A single nerve consists of
several thousand axons - Can be >1m long
- Have phospholipid bilayer
and axoplasm - Surrounded by a nerve sheath
- Sheath usually myelinated
- Myelin= lipid that aids action potential conduction
- Myelin produced by
Schwann cells (PNS) and
oligodendrocytes (CNS) - Nodes of Ranvier every
1mm
CELL COMMUNICATION
- The pre-synaptic
neuron releases
neurotransmitters
into the synapse
which bind to
chemical receptors
on the postsynaptic
neuron
How does a neuron use a change in its resting potential to process and transmit information?
Stimulus, to initial
change in resting
potential——> Neurotransmitters
Flow of ions to transmit
changes in membrane
potential through the
neuron———> Action Potential
Voltage-gated sodium and potassium channels in the plasma
membrane of the axon are primarily responsible for action potentials.
Ion pumps and channels involved
Leakage pores-Open K pores-Maintains resting membrane potential
Gated channels–Open Na gates
Generates action potential
Na/K pumps-Restores membrane
potential
TYPES OF NEURON-
MORPHOLOGY
MULTIPOLAR
- Several dendrites
- 1 axon
BIPOLAR
- 1 dendrite
- 1 axon
UNIPOLAR
- Sensory
- Axon & dendrite fuse as
single process
TYPES OF NEURON :
TYPE OF INFORMATION
- Afferent (sensory)
carry info towards
CNS - Interneuron (local
circuit/association
neurons) - Efferent (motor)
carry info away
from CNS
AFFERENT NEURONS (SENSORY)
- Sensory receptor at peripheral
nerve ending responds to
stimulus and generates action
potential - Long peripheral axon from
receptor to cell body - Cell body usually in PNS
- Short central axon from cell
body to spinal cord
AFFERENT NEURON SENSORY
RECEPTORS
Merkel disc-Touch, pressure
Pacinian corpuscle-Deep pressure
& vibration
Meissner corpuscle-Touch,
pressure
Free nerve endings-Pain,
temperature
EFFERENT NEURONS
(MOTOR)
- Dendrites
- Cell body in CNS
- Efferent axons from
CNS to effector organs
(muscles, glands)
CELL TYPES-
INTERNEURONS
- 99% of all neurons
- CNS only
- Possess dendrites
- Role in reflexes and feedback
loops - E.g. knee jerk
Knee reflex test
PAUL RAPSON/SCIENCE PHOTO LIBRARY
WHITE AND GREY MATTER
WHITE MATTER- AXONS &
SUPPORT CELLS
GREY MATTER- NERVE CELL
BODIES AND SUPPORT CELLS
Luxol fast blue stain- a myelin stain
CLINICAL SIGNIFICANCE-
MULTIPLE SCLEROSIS
- Symptoms appear age 20-40
- Numbness, tingling, blurred
vision, muscle weakness, pain - Autoimmune attack of myelin
- Caused by
genetic/environmental factors - Myelin becomes inflamed then
form lesions - Action potentials slowed, ‘re-
routed’ or blocked
GLIAL CELLS
- Outnumber neurons 3:1
- Maintain synapses &
signalling abilities - Modulate the rate of signal
propagation - Supply nutrients & eliminate
waste - Involved in neural
development - Aid in neuronal recovery
from injury
CNS CELL TYPES-
ASTROCYTES
- Most numerous
- Numerous process which
contact capillaries and
neurons - Provide physical,
metabolic and functional
suppor
CNS GLIA: ROLE OF ASTROCYTES
‘GLUE’
SCAFFOLD
FORMATION OF THE BLOOD BRAIN BARRIER
AID REPAIR
‘MOP UP’ SUBSTANCES
MAINTAINING ENVIRONMENT
SYNAPSE
FORMATION
ASTROCYTES AND THE BLOOD BRAIN BARRIER
Astrocytes are essential for the formation and maintenance of the BBB by providing secreted
factors that lead to the adequate association between the cells of the BBB and the formation of
strong tight junctions.
GFAP (Glial fibrillary acidic
protein) stain
EPENDYMAL CELLS
Lines fluid filled spaces in the
brain. These ciliated glial cells
play a critical role in CSF
homeostasis, brain metabolism
and waste clearance.
Hghly specialised ependymal
cells of the choroid plexus
secrete CSF.
CNS CELL TYPES-
OLIGODENDROCYTES
- Several elongated
projections - Each projection wrapped
around a section of axon
to form a myelin patch - Form CNS myelin sheath
- Enhance nerve impulse
conduction
CNS CELL TYPES-
MICROGLIA
- Radiating branches
- Immune cells of CNS
- Derived from monocytes
- Upon injury/infection
the branches retract,
they become activated
and they migrate to
injury site - Phagocytic scavengers
PNS CELL TYPES-
SCHWANN CELLS
- Encircle PNS axons & form
myelin sheath - 1 schwann cell myelinates a
single axon - Enhance neurotransmission
and participate in axon
regeneration
PNS CELL TYPES-
SATELLITE CELLS
- Flat cells surrounding
cell bodies of
neurons within
GANGLIA - GANGLION= mass of
nerve cell bodies - Regulate material
exchange between
neuronal cell bodies
and interstitial fluid
CLINICAL SIGNIFICANCE-
TUMOURS
- Neurons do not divide,
glial cells do - Most brain tumours
comprise of glial cells
(gliomas)
CLINICAL SIGNIFICANCE-
ALZHEIMER’S DISEASE
- Affects 850,000 people in the
UK alone - Abnormal accumulation of tau
and amyloid-beta protein - Neuronal death and impaired
neurotransmission - Memory loss, cognitive
impairment and personality
changes
