Lecture 8: Introduction to Neural Function Flashcards
Organisation of Nervous System?
- Central Nervous System (CNS)
- Brain and Spinal Cord
- spinal cord;
interneuron: axon terminal, cell body - Peripheral Nervous system;
- nerves and ganglia
- Afferent Neuron: Sensory receptor, peripheral axon (afferent fiber), cell body,central axon,
- Efferent neuron - cell body, axon (efferent fiber), axon terminals, effector organ (muscle or gland)
Organisation of the Nervous System
CNS
- Brain and spinal cord
PNS
Afferent Division (Input to CNS from periphery)
1. Sensory stimuli
2. Visceral stimuli
and
EFFERENT DIVISION (output from CNS to periphery)
1. SOMATIC NERVOUS SYSTEM =
- Motor neurons –> SKELETAL MUSCLES
- AUTONOMIC NERVOUS SYSTEM
- Sympathetic NS = Smooth muscle, cardiac muscle, some endocrine glands and Exocrine glands.
- PARASYMPATHETIC NS = Smooth muscle, cardiac muscle, some endocrine glands and Exocrine glands.
- ENTERIC NERVOUS SYSTEM
Stimuli in digestive tract input — output = digestive organs
Visceral Afferents = 3
- Blood Pressure
- Pain
- Osmolarity
Somatic Afferents = 3
1 * Touch/pain/temp.
2 * Proprioception
3 * Balance
Special senses = 4
1 * Vision
2 * Hearing
3* Taste
4 * Smell
Types of Cells in Nervous System = 2
- Neurons
* main signalling cells
* humans ~1011 neurons - Glial Cells
*support cells (Greek glia,“glue”)
* outnumber neurons 10-50x
Myelin
lipid rich impermeable to ions
Nodes of Ranvier
not covered by myelin
Types of Glial cells
- Microglia
* Phagocytes
* Arise from macrophages outside NS
* Embryologically unrelated to other NS cells - Macroglia
1 * Oligodendrocytes (formation of myelin sheaths CNS)
2 * Schwann cells (formation of myelin sheaths PNS)
3 * Astrocytes (blood-brain barrier, reuptake transmitters)
- Ependymal cell
Function of Glial Cells =7
1 ➢Structural support and insulation of neurons
2 ➢Myelin sheaths - Oligodendrocytes & Schwann cells
3 ➢Scavenging dead cells - microglia
4 ➢Uptake of released neurotransmitters, buffer for excess K+
5 ➢Blood brain barrier- astrocytes + endothelial cells
6 ➢Glia direct migration of developing neurons
7 ➢ Trophic support for neurons
Typical NEURON structure AND ROLE.
- Dendrites = input
- Soma = Integrative
- Axon = conductile
- Axon terminals = output
SECRETION
How to — Classification of Neurons = 6
1 * Number of neurites
2 * Size
3 * Shape
4 * Neurochemistry
5 * Location
6 * Connectivity
Morphological Variations
- Unipolar cell
- dendrite
- axon
- cell body
INVERTEBRATE NEURON - Pseudo-unipolar cell
- dendrite, central axon, single process, cell body, peripheral axon to skin and muscle
DORSAL ROOT GANGLION CELL - BIPOLAR CELL
- dendrites, cell body, axon,
RETINAL BIPOLAR CELL - 3 TYPES OF MULTIPOLAR CELLS
- Spinal motor neuron
- Hippocampal pyramidal cell
- Purkinje cell of cerebellum
Structure of Nerve Cells = 7
1 ➢Nerve cells are NEURONS
2 ➢ The cell body is called the SOMA
3 ➢Projections from the soma are NEURITES
4 ➢DENDRITES are neurites which receive input
5 ➢AXONSs transmit signal long distances
6 ➢ TERMINALS are where neurotransmitters are released from
7 ➢ NEUROTRANSMITTERS are the chemicals that signal between nerve cells
UNDERSTANDING Neural Signalling = 3
- Nerve to nerve connection is a SYNAPSES
- Neve to gland or muscle is a JUNCTION
- very close contacts between axon terminals and target cell
NEURAL SIGNALLING = PRE-SYNAPTIC VS POST-SYNAPTIC
Pre-synaptic cell sends the signal
Post-synaptic cell receives the signal
Signalling Between Neurons
- Axosomatic synapses
- Axodendritic synapses
- Axo-axonic synapse
Neuronal Signalling = RESTING MEMBRANE POTENTIAL (-60 TO -70 mV)
WHY = 2
Resting membrane potential (-60 to -70 mV)
DUE TO
1 * unequal distribution electrically charged ions
2 * selective permeability of membrane these ions
In nerve cells membrane potential can be quickly altered by
changes in permeability to certain ions.
Recording Membrane Potential
Intracellular recordings enable measurement of membrane potential
Amplifier and oscilloscope – extracellular electrode
y axis = Vm (mV)
x axis = time
Passive vs Active response
Understanding PASSIVE SIGNALS
GRADED VS ACTION POTENTIALS
—Changes in potential are used to transmit information within the nervous system
GRADED POTENTIALS signal over short distances
- ACTION POTENTIALS signal over long distances
Understanding PASSIVE SIGNALS = 3
- Vm decays due to leakage of electrically charged ions.
- Distance at which Vm has decayed to 37% of original value at current injection defines length constant (λ).
- λ is a measure of efficiency of passive spread.
“Because changes in potential “die out” over short distances (few mm) they only signal over short distances”
UNDERSTANDING AXON HILLOCK = 4
The axon hillock is the region of a neuron that controls the initiation of an electrical impulse based on the inputs from other neurons or the environment.
- THRESHOLD for action potential lowest at AXON HILLOCK
- Axon hillock highest density of Na+ channels
- Effectiveness of synaptic connection depends on the distance length constant
- Integration of all EXCITATORY and INHIBITORY inputs
Summation
The less a passive signal decays, the more likely it is to generate an AP
Temporal vs Spatial summation
- Synaptic current,
- Synaptic potential,
-long time constant (100msec) vs long length constant (1nm)
- short time constant (20 msec) vs short length (0.1 nm)
Neuronal Connectivity = 2
- Divergence
- Convergence Excitation and excitation (E) - Convergence
- Convergence excitation (E) and Inhibition (I)
Interneurons: Feed forward inhibition
- Afferent neurons innervating extensor muscles
- Extensor motor neuron to extensors
or
1.Afferent neurons innervating extensor muscles
2. Inhibitory interneuron
3. Afferent innervating flexor muscles
3. flexor motor neuron
4. flexors
INTERNEURONS: Feedback inhibition
1.Afferent neurons innervating extensor muscles
2. Extensor motor neuron
or 1.Afferent neurons innervating extensor muscles
2. Inhibitory interneuron
INTERNEURON = GATING INTERNEURONS
- SELECTABLE INPUT
- DESCENDING CONTROL SIGNAL
- INTERNEURON
- MOTOR NEURON
- + other inputs
interneuron = Gating by presynaptic inhibition
- selectable input
- descending control signal
- interneuron or motor neuron
Summary = 7
1 ➢ The nervous system has central and peripheral components with afferent and efferent neurons.
2 ➢ Nerve tissue contains both neurons and glial cells
3 ➢ Signalling occurs between neurons at synapses
4 ➢ Signals can cause either excitation or inhibition of the post synaptic cell
5 ➢ Signals received at the dendrites and soma are integrated at the axon hillock where action potentials are generated
6 ➢ Action potentials are regenerated signals that travel the length of the axon
7 ➢ Neural pathways show both divergence and convergence
