Cells and tissue of the nervous system Flashcards
What are the divisions of the nervous system?
CNS (brain and spinal cord) –> PNS (spinal and cranial nerves) –> sensory (afferent) and motor (efferent)
Motor (efferent) –> somatic (voluntary) and autonomic (involuntary)
Autonomic (involuntary) –> sympathetic and parasympathetic
What are the 2 main cell types?
1) Neurons: structural and functional unit; excitable cells; impulses carried as AP’s
2) Glial cells: non-excitable supporting cells that are much smaller than neurons
In which direction do impulses travel down a neuron?
From cell body to synaptic terminal.
What happens long term if a neuron is damaged?
Axons can grow back if they are damaged - lots of ER in the cytoplasm so can make new proteins etc.
However, if the neuronal cell body in the spinal cord is damaged this is irreversible.
What are the 2 main forms of neurons?
Sensory (dorsal) or motor (ventral).
Sensory neurones have their cell bodies outside of the CNS in the dorsal root ganglion of the spinal cord.
What is the function of the myelin sheath in axons?
To increase conduction speed in axons by saltatory conduction - ion flow only occurs at the nodes of Ranvier which are the spaces between the myelin cells. Neurons can be myelinated or non-myelinated.
Which cells form the myelin sheath in the CNS and PNS?
Oligodendrocytes in the CNS.
Schwann cells in the PNS.
How do Schwann cells myelinate axons in the PNS?
They wrap themselves around axons to form a mesaxon - the cytoplasm of the
Schwann cell gets extruded and only the cell membrane remains.
What is in the white and grey matter of the CNS?
White matter - myelinated axons.
Grey matter - cell bodies.
What is seen in axons in MS?
Patchy loss/scarring of the myelin sheath (demyelination). This leads to abnormal nerve conduction across affected axons.
What are the 2 types of multipolar neurons??
1) Motor neurones
2) Interneurones (transmits impulses between other neurons, especially as part of a reflex arc)
What are the 2 types of bipolar neurons?
1) Olfactory mucosa
2) Retinal nerve fibres
Which neurons are pseudounipolar?
Sensory neurons - one branch runs to the periphery and one to the spinal cord (the axon has split in 2).
Where are the cell bodies of motor neurones?
The ventral horn of the spinal cord.
In the PNS, where do white and grey matter go?
White matter - myelinated axons form nerves.
Grey matter - cell bodies form ganglia
In the CNS, where do white and grey matter go?
Collections of myelinated axons form white matter (diffuse) or tracts (bundles of axons carrying specific info in the white matter).
Cell bodies and non-myelinated axons form grey matter (diffuse) or nuclei (localised)
What happens when cutaneous receptors in the skin sense pain?
A pseudounipolar sensory neuron travels through the dorsal root ganglion and ascends via white fibre tracts to the brain where it reaches a collection of neuronal cell bodies (nucleus).
How many types of glial cells are there?
6 different types - astrocytes are the most common.
What does the diencephalon contain?
Thalamus, hypothalamus and pituitary gland (posterior).
Describe neural tube formation.
The top layer of the embryo (surface ectoderm) has thickened by day 18 - this is the neural plate) This thickens further, folds over and becomes the neural tube.
Neural tube divides into 3 primary vesicles in weeks 4, then into secondary vesicles in week 5. These develop into the adult brain.
What happens to the forebrain?
There are 2 secondary vesicles formed:
- Telencephalon which becomes the cerebrum
- Diencephalon which the eyes develop from (optic cups at either side)
Which structures come from the hindbrain?
Cerebellum and brainstem.
Where do the ventricles of the adult brain arise from?
The neural tube has a cavity which persists in the adult brain. This cavity becomes a series of interconnected ventricles.
What do the ventricles contain?
CSF
