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
Where are the lateral ventricles?
These are C-shaped cavities that lie in the cerebral hemispheres.
Which structure connects the lateral ventricles to the 3rd ventricle?
The interventricular foramen of Munro.
Where does the 3rd ventricle lie?
Within the diencephalon.
What is the cerebral aqueduct?
Connects the 3rd ventricle with the 4th ventricle.
Where does the 4th ventricle lie?
In the hindbrain. It is diamond-shaped.
What are the 3 meninges?
1) Dura mater - outermost layer; tough, fibrous and has dural folds
2) Arachnoid mater - middle layer
3) Pia mater - innermost layer; vascularised and dips into the folds of the brain
What does the subarachnoid space contain?
CSF
What is the subdural space?
A potential space between the dura and arachnoid mater - they can be separated in trauma and blood can collect here (subdural haematoma).
Where is CSF produced?
The choroid plexus of the ventricles (mainly lateral ventricles as they are the biggest).
How is CSF reabsorbed into the venous circulation?
Via arachnoid granulations which are present in the dural sinuses of the brain.
How are drugs delivered to the CNS?
They need to cross the BBB - need to be lipid soluble or use a suitable vector.
What is the function of the BBB?
Maintains homeostasis in the brain parenchyma to protect the brain from harmful AA’s/ions that are present in the blood stream.
What makes up the BBB?
Endothelium - tight junction
Thick basal lamina
Foot processes of astrocytes
Where is the BBB absent?
In a few circumventricular organs - parts of the hypothalamus and posterior pituitary.
