49 Nervous System Flashcards
How many neutrons are there in the human brain?
Around 100 billion
What are the simplest animals with nervous system?
Cnidarians like Hydras and Jellies.
In what animals are distinct nervous systems seen?
Hydra, Sea stars, Planarians (flat worms), Leeches, Insects, Chitons (molluscs), Squid (molluscs) and Salamanders
What is the structure of the nervous systems of Hydras?
Interconnected nerve cells form a diffuse “nerve net” which controls the contraction and expansion of the gastrovascular cavity.
Unlike the nervous systems of other animals it lacks clusters of neurons that perform specialised tasks.
They also differ in the the ’nerve net’ is a net of individual axons, not nerves which are multiple axons bundled together.
What is the structure of the nervous systems of Sea stars?
They have a set of radial nerves connecting to a central nerve ring. Within each arm of a sea star, the radial nerve is linked to a nerve net from which it receives input and to which it sends signals controlling muscle contraction.
What is the structure of the nervous systems of Planarians (flatworms)?
They have a very small brain that leads to two longitudinal nerve cords that pass from the anterior (front) end to the posterior.
Along the length of these nerve cords they are connected by transverse nerves (the ‘rungs of a ladder’) to form a ladder-shpaed structure
What is the structure of the nervous systems of Leeches (annelids)?
They have a brain at the anterior end and a ‘ventral nerve cord’ that travels down to the posterior end.
Throughout the entire length of this ‘ventral nerve cord’ are ’segmental ganglia’ which act as processing centres along with the brain.
What is the structure of the nervous systems of Insects?
Like leeches they have a brain at the anterior end and a ‘ventral nerve cord’ that travels down to the posterior end.
Throughout the entire length of this ‘ventral nerve cord’ are ’segmental ganglia’ which act as processing centres along with the brain.
What is the structure of the nervous systems of Chitons (molluscs)?
They do not have a fully centralised brain but instead have a small ‘anterior nerve ring’ with many ganglia.
Nerve fibres extend from the nerve ring laterally. These are bridged by ‘longitudinal nerve cord.’
What is the structure of the nervous systems of Squid (molluscs)?
They have a highly advanced nervous system with an anterior brain and nerves that extend through the body. Some ganglia are seen on nerves out side the brain.
What is the structure of the nervous systems of Salamanders?
They have a brain that leads to a spinal cord (also called the dorsal nerve cord)
Along this spinal cord are sensory ganglia.
What are ‘ganglia’s?
A concentration of grey matter in the PNS that act as processing centres. (Basal ganglia are not true ganglia as they are in the CNS)
What do nerves do?
They channel and organize information that flows along specific routes through the nervous system.
What is a pattern seen in the nervous systems of bilaterally symmetrical organisms?
They exhibit ‘cephalisation’ which is an evolutionary trend towards a clustering of sensory neutrons and interneurons at the anterior (front) of the organism.
Chitons and squid are both molluscs but have vastly different nervous systems. What explains this?
Chitons are slow and sessile so have simpler nervous systems than predatory molluscs like squid and octopus which also have advanced eyes.
How do the nervous systems of vertebrates differ from that of invertebrates?
Vertebrates have spinal cords not nerve cords.
Vertebrates also differ in that they have distinct CNS and PNS.
What does “nuclei’ refer to with regard to the nervous system?
A group of neuron like a ganglia but that are in the CNS (ganglia are by definition PNS)
What is the purpose of the spinal cord?
To carry signals to and from the brain and to initiate reflexes.
What is an example of a reflex?
The knee jerk reaction.
How does the nerve cord’s location differ between vertebrate and invertebrates?
In vertebrates it is located dorsally (on the back) whereas in many invertebrates it is located ventrally (on the front) for protection when crawling.
What happens during the ‘knee-jerk reaction’?
The reflex is initiated artificially by tapping the tendon connected to the
quadriceps muscle. Mechanoreceptors detect a sudden stretch in the quadriceps, This signal is conveyed by sensory neurons to the spinal cord
In response to signals from the sensory neurons, motor neurons in the spinal cord convey signals to the quadriceps, causing it to contract and jerking the lower leg forward.
Sensory neurons also communicate with interneurons in the spinal cord. The interneurons inhibit motor neurons that lead to the hamstring muscle. This inhibition prevents contraction of the hamstring, which would resist the action of the quadriceps.
Where is the knee-jerk reaction seen naturally?
When someone is carrying a large load. If their knees begin to buckle the knee-jerk reaction holds the knees in place.
What is the basic structure of the brain?
It has a folded outer layer called the cortex that consists of grey matter.
On the inside of the brain is white matter.
At the very centre of the brain is are ventricles that are filled by cerebrospinal fluid.
What does the central nervous system develop from?
The ‘hollow dorsal nerve cord’
What happens to the hollow interior of the ‘hollow dorsal nerve cord’ when the embryo develops?
It becomes the ventricles and the “central canal” of the spinal cord.
Both of these are filled with cerebrospinal fluid.
How is cerebrospinal fluid produced?
By the brain which forms it by filtering blood from the arteries.
What happens to cerebrospinal fluid once it is in the brain?
It circulates through the central canal of the spinal cord and the brain’s ventricles before draining into veins.
What is the importance of the cerebrospinal fluid?
It supplies the brain with nutrients and hormones and carries away wastes.
In mammals, the cerebrospinal fluid also cushions the brain and spinal cord by circulating between layers of connective tissue that surround the CNS.
What surrounds the ventricles of the brain and what is its function?
Ependymal cells that have cilia too promote the circulation of cerebrospinal fluid.
What are some specific types of glial cells?
Oligodendrocytes, Schwann cells, microglia, astrocytes and radial glia
What are microglia?
Glial cells that are actually immune cells who protect the brain from pathogens.
What are astrocytes?
Glial cells that facilitate information transfer at synapses and in some instances release neurotransmitters.
Astrocytes next to active neurons cause nearby blood vessels to dilate, increasing blood flow and enabling the neurons to obtain oxygen and glucose more quickly.
Astrocytes also regulate extracellular concentrations of ions and neurotransmitters.
What are radial glia?
Glial cells found in embryos. They form tracks along which newly formed neurons migrate from the neural tube, the structure that gives rise to the CNS
How can neurons be regenerated?
By radial glia and astrocytes which can act as stem cells to generate new neurons and glia.
Astrocytes facilitate information transfer, dilate blood vessels and regulate the extracellular environment.
What other function do they have?
Astrocytes induce cells that line the capillaries to form tight junctions. This regulates what substances can leave the capillary as it passes through the brain.
This is called the ‘blood-brain barrier’ and helps prevent pathogens from entering the brain.
What is the spinal cord divided into?
From anterior to posterior:
Cervical, Thoracic, Lumbar, Sacral
What do afferent neurons do?
Carry signals to the brain
What do efferent neurons do?
Carry signals away from the brain.
What do afferent neurons carry signals from?
Sensory receptors
What system do efferent neurons lead to?
The motor system and the autonomic system
What does the motor system do?
Controls skeletal muscles.
What does the autonomic system do?
Controls involuntary actions. such as smooth muscles, cardiac muscle, glands and organs
What is the autonomic system divided into?
The sympathetic division, the parasympathetic division and the enteric division.
What is the fundamental purpose of the sympathetic division?
To mobilise energy resources, increase circulation and otherwise increase the body’s ability to ‘fight of flight’
What is the fundamental purpose of the parasympathetic division?
To counter the sympathetic division and thus conserve the body’s resources.
What are the specific responses to activation of the parasympathetic division?
Constricts pupil of eye
Stimulates salivary gland secretion
Constricts bronchi in lungs (reduces airflow)
Slows heart
Stimulates activity of the stomach and intestines
Stimulates activity of the pancreas
Stimulates gallbladder
Promotes emptying of the bladder
Promotes erection of the genitalia]
(total: 9)
What are the specific responses to activation of the sympathetic division?
Dilates pupil of eye
Inhibits salivary gland secretion
Relaxes bronchi in lungs causing them to dilate and thus increasing air flow.

Accelerates heart
Inhibits activity of stomach and intestines

Inhibits activity of pancreas

Stimulates glucose release from liver; inhibits gallbladder
Stimulates adrenal medulla to secrete epinephrine and norepinephrine.

Inhibits emptying of bladder

Promotes ejaculation and vaginal contractions
What is the enteric division of the nervous system?
The division which regulates the digestive system i.e peristalsis.
The enteric division is also regulates by the sympathetic and parasympathetic systems but can function on its owns.
When the brain first forms what does it consist of?
A forebrain, mid brain and hind brain.
In an embryo at 5 weeks, what has the forebrain become?
A ’telencephalon’ and a ‘diencephalon’
In an embryo at 5 weeks, what has the midbrain become?
The ‘mesencephalon’
In an embryo at 5 weeks, what has the hindbrain become?
The ‘metencephalon’ and the ‘mylencephalon’
What does the telencephalon become?
The cerebrum (includes cerebral cortex, white matter, basal nuclei)
What does the diencephalon become?
It becomes a developed diencephalon which includes the thalamus, hypothalamus and epithalamus
What does the mesencephalon become?
The midbrain (part of brainstem)
What does the metencephalon become?
The pons (part of brainstem) and the cerebellum
What does the myelencephalon become?
The medulla oblongata (part of brain stem)
What does the Cerebrum arise from?
The telencephalon from the forebrain
What does the Diencephalon arise from?
The diencephalon from the forebrain
What does the Midbrain arise from?
The mesencephalon from the midbrain
What does the Pons arise from?
The metencephalon from the hind brain
What does the Cerebellum arise from?
The metencephalon from the hind brain
