Cell Neuro Exam 1

Patellar stretch reflex

1. Detect the stretch (+ and electrical potential changes)

   1. A sensory neuron, which lives in ganglion (specifically the dorsal root ganglion), detects the stretch

   2. The sensory neuron sends a neurite or process out to the muscle

   3. The muscle stretch activates this neurite and causes it to have an electrical charge (electrical potential across membrane)

   4. When the sensory out in muscle stretched, ion channels open, ions move across membrane (causing depolarization), electrical potential of the sensory neuron changes, and may make an action potential if the depolarization reaches the threshold potential

2. Action potential is generated in the sensory neuron and travels in a nerve

3. The action potential reaches the CNS

   1. The signal passes across a synapse because it must be transmitted to another neuron

   2. The sensory neuron is the presynaptic synapse/neuron and the next neuron is the postsynaptic neuron

      1. At a synapse, the presynaptic neuron releases neurotransmitters into the postsynaptic cleft, where it diffuses to the postsynaptic neuron membrane. The neurotransmitters open ion channels to change the electrical potential on the postsynaptic neuron.

      2. Synapse takes place at the receiving end of the next neuron, at its dendrites

4. The postsynaptic cell (in this case) is called a motor neuron, which synapses with muscles and makes them contract

5. The motor neuron generates an action potential, which travels along the axon of the motor neuron, which is inside a bundle of axons (nerve). 

   1. The motor neuron (presynaptic) makes a synapse on the muscle (postsynaptic)

   2. The muscle opens ion channels and the membrane potential changes. The muscle responds to the change in membrane potential by contracting

6. Leg swings out

Patellar stretch drawing

Presynaptic and postsynaptic of patellar stretch

The presynaptic is the sensory neuron and the postsynaptic is the motor neuron

Ganglion

localized, dense cluster of neuronal bodies that acts as a processing or relay center

Nerve

a bundle of neurons

Neurite

any projection or extension from the cell body of a neuron, which can develop into either an axon or a dendrite

Motor neuron

synapse with muscles and make them contract

Afferent

signal or neurite going towards the cell body (to the CNS)

Efferent

signal or neurite going away from the cell body (or CNS)

Neurons

cells. They have all the typical organelles, but their membranes are designed to send and receive electrical signals. 

• Their shapes are highly variable depending on their purpose

Categories of neurons

sensory neurons, motor neurons, interneurons

Sensory neurons

respond to environmental signals such as light and sound

Motor neurons

send signals to muscles

Interneurons

send signals between sensory, motor, and other interneurons

5 major types of glial cells

astrocytes, radial glial, microglia, oligodendrocytes, Schwann cells

Astrocytes

they are physical support for neurons and regulate K⁺ concentrations in the extracellular space. They have some nutritive function and remove neurotransmitters from the extracellular space.

What are the most common glial cells int he brain?

astrocytes, which are important fro the blood brain barrier

Radial glial

Important in development. They form a scaffold for neurons to climb during development

What glial cell is most common in neurodegenerative diseases like Parkinsons?

Microglia. It is not entirely clear if these are good or bad

Microglia

cleanup cellular debris if there’s damage and show up when there is an infection or problems as part of immune function. Made in bone marrow. They remove extra synapses during development.

Myelin producing glial cells

Oligodendrocytes and Schwann cells

Oligodendrocytes

Found in the brain and spinal cord (CNS). They wrap around axons of nerve cells with myelin

Inhibit actual nerve regrowth but support myelin repair

Schwann cells

Found in peripheral nerves (not CNS). Whole schwann cells wrap around an axon. If there is nerve damage, they can form a guide for axons to regenerate. Can promote neuronal outgrowth by secreting something

Only glial cell not found in the CNS

Schwann cells

Invertebrate nerve net

a simple, decentralized nervous system made of interconnected neurons spread across the body without a brain or central control center

• The simplest neuronal organization (ex: in jellyfish) with no CNS or PNS

• Spreads out like a wave

• Different from ganglion

Myelin

The cell membrane of glial cells. Glial cells wrap many times around the axon tightly to squeeze out cytoplasm, so myelin is basically many layers of the cell membrane stacked on itself. It is an insulator, speeding up action potentials.

Insulator

allows for faster propagation of action potentials

Nodes of Ranvier

gaps in the myelin that contain action potentials to recharge and boost the action potential as it moves along

Rostral, anterior

towards the nose

caudal, posterior

towards the tails

dorsal

along the back

ventral

towards the belly

lateral

away from the midline

medial

towards the midline

proximal

close to the structure noted

distal

away from the structure noted

distal

away from the structure noted

superior

above (like dorsal in a cat) - brain specific

inferior

below (like ventral in a cat) - brain specific

sagittal section

makes two mirror images

frontal or coronal section

cuts between the front and back

horizontal section

splits into top half and bottom half

How does the nervous system develop?

Nervous system begins as a tube anteriormost and becomes the forebrain. The middle region is the mid brain and the posterior parts of develop the hindbrain.

Image of nervous system development

Forebrain components

Telencephalon and Diencephalon

Telencephalon purpose

performs higher mental functions, philosophizing, processing sensory information, and motor control

Telencephalon components

Cerebral cortex (includes 4 lobes), basal ganglia, limbic system - amygdala and hippocampus, nucleus accumbens, olfactory bulb

Brain lobes

• Frontal lobe (higher thoughts and self control)

• Parietal lobe

• Occipital lobe (visual processing)

• Temporal lobe (hearing and speech)

  

basal ganglia

important for planning movement and postural adjustmnets

limbic system

• Amygdala: emotional behaviors like rage, fear, repulsion

• Hippocampus: memory making and storage

Story of HM, Henry Molaison

HM had seizures so they took out his hippocampus and from then on he could not make memories

Amygdala

Emotional behaviors like rage, fear, repulsion

Hippocampus

Memory making and storage

Nucleus accumbens

reward/pleasure circuit

Olfactory bulb

Processes information about smells

Diencephalon purpose

Major relay, integration, and control center

Diencephalon components

Thalamus - lateral and medial geniculate, and hypothalamus

thalamus

• processes and sorts sensory and motor information before sending it to the brain-telencephalon

  • includes lateral and medial geniculate

lateral geniculate

first step in visual processing from the retina

medial geniculate

Processing from the ears

Hypothalamus

regulates hormone secretion by the pituitary gland

• Important for homeostasis - triggers behaviors to keep consistent (temp, bp, hydration, salt)

Midbrain

Mesencephalon

Mesencephalon components

inferior and superior colliculi, and substantia nigra

Inferior colliculus

Auditory information

Superior colliculi

Visual information

Substantia nigra

for posture and motor control (damaged in Parkinsons)

Hindbrain components

Metencephalon and Myelencephalon

Metencephalon components

Pons and cerebellum

Pons

Superhighway of pathways. It communicates with cerebellum

• Major tract of axons especially going to and from the cerebellum

• Includes collections of ganglia that are important in basic functions like sleep, wakefulness, and respirations

Cerebellum

Coordinating movement

• Highly convoluted and important for muscle tone, balance, carrying out movements smoothly, and motor memory

• Takes information from the telencephalon (what to do) then it corrects what you did to make motor memory

Myelencephalon components

medulla

Medulla

Continuous with the spinal cord and controls basic functions like bp, coughing, laughing, and heart rate

Cerebellar cells

Purkinje cells, mossy fibers, and climbing fibers

Purkinje cells (input and output?)

• Input: receive information on what was the intended movement (mossy fibers) and what was the actual movement (climbing fibers)

• Output: corrections if needed of movement to match what was intended - correct motor error

  • Output is inhibitory of deep cerebellar nuclei and from there ends in the cerebral cortex

Mossy fibers

Axons coming from the pons and bring information on intended movement

• Synapse with granule cells and then to parallel fibers to reach purkinje

Climbing fibers

come from medulla and bring information on the actual movement

Purkinje cell drawing

Spinal cord transverse section

Gray matter

cell bodies of neurons, including the dorsal horn and ventral horn

dorsal horn

sensory

ventral horn

motor

white matter

myelin surrounding axons

central canal

• Canals/ventricles are filled with cerebrospinal fluid (CSF)

• Illustrates the tubular origins of the CNS

• In the brain the central canal expands and gets distorted but is there as the brain ventricles

Meninges

supports the CNS, has places to pull out CSF and return fluid to the circulatory system, and contains the choroid plexus

Choroid plexus

full of capillaries that produce the CSF

Endothelial cells of capillaries

In the innermost layer of a blood vessel and joined by tight junctions - BBB

Blood Brain Barrier

tight regulation of what goes form the blood to neural tissue of the brain

What can cross the blood brain barrier?

Lipid soluble items, and items attached to glucose to pass through glucose pumps, and a new method includes attaching to nanobeads

Astrocytes and the meninges

Astrocytes extend “feet” that sit on capillaries. These can secrete molecular signals to capillary cells to tighter or loosen the tight junctions.

Cerebrospinal fluid

Circulates within and around the CNS held there by a set of meninges

• Contains ions/salts in proper concentrations for good neural function, also a  few proteins

Components of the peripheral nervous system

somatic and autonomic

components of autonomic nervous system

sympathetic, parasympathetic, enteric

sympathetic nervous system

Fight, flight, fright. Short preganglionic fiber terminates in sympathetic ganglion, using acetylcholine (ACh) as a neurotransmitter. It makes a synapse with postganglionic fiber cell, which extends out to the organ or tissue where it makes a synapse using norepinephrine (NE) neurotransmitter

Parasympathetic nervous system

• Cell bodies in brain or lower spinal cord

• Send a long preganglionic fiver to a ganglion out near the organ innervated synapse with the postganglionic fiber neuron, using ACh as the neurotransmitter. The postganglionic fibers neuron releases ACh at the organ

Enteric nervous system

• Network on the gut with many ganglia

• Large number of neurotransmitters and many different types

  • Subject to regulation by sympathetic and parasympathetic nervous systems

Ion channel proteins

• Leakage channels: open most of the time

• Some open under certain conditions

  • Ligand gated channels: a molecule binds to them

  • Voltage gated channels: membrane has a voltage change

  • Stretch sensitive channels: open when they are physically stretched or moved

• Ion channel proteins twist and squirm due to thermal energy and they will randomly open and close at all times

  • So when we say the channels are open, we mean that the probability that one of these channels is open is very high