Nervous System Flashcards
Key characteristics of general sensory organs
-Widespread throughout body
-Detect touch and temperature
-Role in proprioception
Key characteristics of special sensory organs
-Localised to a small area
-Highly specialised
Encapsulated sensory receptor
-Mechanoreceptor
-Sensitive to touch, pressure, vibration, temperature
-Located in dermis and pancreas
Examples of encapsulated sensory receptors
-Meissner’s corpuscles
-Pacinian corpuscles
-Ruffini’s corpuscles
-Merkel’s discs
Free sensory receptor
-Nociceptors, mechanoreceptors and chemoreceptors
-Detects pain and other noxious stimuli
-Located in high sensitivity areas (intestines, tooth pulp, skin, oral cavity, cornea)
Associated sensory receptor
-Sensitivity relies on association with another structure eg hair, muscle spindle
-Detects mechanical or proprioceptive stimuli
Functions of proprioception
-Automatic postural adjustment
-Pre-activates muscles in preparation (for a fall, landing etc)
Muscle spindle proprioceptors
-Intrafusal muscle fibres and associated sensory receptors
-Measure muscle length and rate of muscle length change
-Responsible for stretch reflex
Stretch reflex
Spinal reflex which regulates resting muscle tone according to muscle length detected by muscle spindles
Golgi tendon organs
-Detect tension within tendons
-Located in tendons attached to skeletal muscle
Gustatory cells
-Primary chemoreceptors
-Located in taste buds
-Have no axons
-Impulses relayed by 3 cranial nerves
Vomeronasal organ
-Detects pheromones
-Separate and parallel to main olfactory pathway
-Connected to mouth and nose by nasopalatine canal
-Animals exhibit mouth/lip movements to actively draw air over the organ
Fovea
Area of high cone cell density within the retina
Pineal complex
Primitive light-sensing organ within the brain. Conserved by turtles, which use it to detect day/night and seasonal variations in sunlight
Magnetoreception
Some migrating animals are able to navigate by sensing minute variations in Earth’s magnetic field, used as an “internal compass”
Neuromast organ
-Common mechanoreceptor setup
-Consists of hair cells and support cells covered by a gelatinous cap
-Used in lateral line system
How do animals use hair cells to detect changes in their environment?
-Fish use hair cells as part of their lateral line system to measure water flow and detect objects at a distance
-Mammals use hair cells as part of their vestibular system to detect their own movement
-Mammals use hair cells in the cochlea to detect sound
Function of corticospinal pathway in mammals
Fine control of hands, particularly individual finger movements
Function of tectospinal pathway in mammals
-Co-ordinated locomotor and feeding movements
-Head turning reflex
-Postural movement reflexes (in response to visual stimuli)
Function of rubrospinal pathway in mammals
-Motor function
-Flexor muscle activity
-Extensor muscle inhibition
Function of vestibulospinal pathway in mammals
-Extensor muscle activity
-Postural reflexes
-Equilibrium maintaining reflexes (in response to vestibular input)
Function of reticulospinal pathway in mammals
-Gross movement (locomotion, posture, reaching)
-Proximal and axial muscle control
Which descending pathway would a person use when carrying out complex surgery?
Corticospinal pathway
Three layers of the eye
Retina, choroid, sclera
Function of pit organ in snakes such as pit vipers
Infrared light receptor for heat detection
What phylogenetic precursor does the vestibular system arise from?
The lateral line system
How do the vestibular canals detect rotation?
Inertia causes fluid in the semicircular canals to lag behind the canal itself. The resulting movement of fluid relative to the canal walls stimulates hair cells in the crista wall.
How many semicircular canals do mammals have?
Three: one in each axis
Name the three semicircular canals of the vestibular system
Anterior, posterior and horizontal
Structure of the organ of Corti
Strip of highly specialised neuromasts, connected to the brain via the auditory nerve
Adaptations of the owl for directional hearing
-Facial ruff of feathers channels sound similarly to the mammalian pinna
-Asymmetrical external auditory canals capture sound multidirectionally
-Measurement of Interaural Loudness Difference allows sounds to be located in the horizontal plane
Mechanoreceptive specialisations of the star-nosed mole
-Nostrils are surrounded by 22 appendages covered in mechanoreceptor organs called Eimer’s organs.
-Eimer’s organs are raised domes 30-50um across, consisting of free nerve endings, a Merkel’s disc and a lamellated corpuscle
-Mechanoreceptors are densest at distal end of appendage
Ipsilateral
On the same side of the brain
Contralateral
On the opposite side of the brain
Role of the CNS
Receives information from sensory receptors, processes this and sends information to effectors in order to co-ordinate activities and responses necessary for survival and reproduction.
What does the inner space of the neural tube form?
The ventricular system
What does the neural crest give rise to?
The peripheral nervous system
What does the telencephalon give rise to?
Cerebral hemispheres
From which embryonic structure does the hypothalamus arise?
Diencephalon
The three white matter systems are:
-Corpus callosum
-Cortical white matter
-Internal capsule
Where do sensory pathways from the eyes, ears and skin relay before terminating in the cerebral cortex?
The thalamus
What two structures does the diencephalon give rise to?
The thalamus and hypothalamus
What regulates the autonomic nervous system?
The hypothalamus
What does the dorsal surface of the mesencephalon differentiate into?
The tectum
What does the floor of the mesencephalon differentiate into?
The tegmentum
What structures does the rostral rhombencephalon (metencephalon) form?
The cerebellum and pons
What embryonic structure does the cerebellum form from?
The rhombic lips
What structure does the caudal rhombencephalon (myelencephalon) form?
The medulla
Function of the pyramidal decussation
Pyramidal tracts cross the midline where the medulla meets the spinal cord, meaning that the cortex of one brain hemisphere controls movement on the opposite side of the body
Function of the dorsal horn
Receives sensory inputs from dorsal root fibres
Function of the ventral horn
Sends motor outputs to ventral routes which innervate muscles
Haeckel embryology theory
Developmental stages recapitulate adult evolution (eg in frog development, fish characteristics are made, then frog characteristics) (WRONG)
Von Baer embryology theory
Developmental stages do not recapitulate adult evolution
Which germ layer develops into the CNS?
Ectoderm
How many layers do the meninges of the fish have?
One.
The three layers of the mammalian meninges
-Dura mater
-Arachnoid layer
-Pia mater
How many layers do the meninges of amphibians, reptiles and birds have?
Two
Two major functions of spinal cord
-Execute spinal reflexes
-Carry converging and diverging information (whatever that means)
Two main ascending tracts of the spinal cord
Fasciculus gracilis and fasciculus cuneatus (both carry proprioception info)
What part of the brain is shrunk in blind cave fish?
The optic tectum
Where are the major centres for involuntary reflexes located?
The medulla oblongata
Function of the Pons
Relays sensory and motor tracts between cerebral cortex and cerebellar cortex
Functions of cerebellum
-Maintaining equilibrium
-Refines motor activity
What is the largest area of the brain in fish and amphibians?
The midbrain
Where is the pineal gland located?
In the epithalamus
Role of the dorsal thalamus
Co-ordinating centre of sensory inputs from all over the body
Where are the basal ganglia located?
The base of both cerebral hemispheres
What would happen if you removed an animal’s cerebellum?
-Failure to maintain equilibrium
-Poorer co-ordination
Where does sensory information enter the spinal cord?
Dorsal horn
Function of the medulla oblongata
-Location of primary nuclei for some cranial nerves
-Major route of passage for ascending and descending spinal pathways
-Major centre for involuntary reflexes
Does the cerebellum initiate motor output?
No, it only modifies and refines motor outputs.
Components of the epithalamus
Pineal gland and habenular nucleus
Function of the hypothalamus
Regulates homeostasis
Function of dorsal thalamus
Receives and co-ordinates sensory inputs
Gyri
Folds of the Cortex
Function of the corpus callosum
Connects left and right brain hemispheres
Building blocks of the peripheral nervous system
-Neurons
-Nerves
-Ganglia
-Pathways
-Circuits
Evolutionary origin of the CNS
Dorsal hollow nerve tube
Chordate synapomorphies
-Pharyngeal slits (precursor to head organisation)
-Notochord
-Dorsal hollow nerve tube (precursor to CNS)
-Endostyle (precursor to thyroid
-Post-anal tail
Vertebrate synapomorphies
-Vertebral column
-Cranium
-Neural crest
-Neurogenic placodes
-Brain with 3 divisions
-Hypothalamus-pituitary system
Components of nervous system segments
Vertebra, spinal nerve, muscle
Key characteristics of somatic PNS
-Innervates muscles, skin and their derivatives
-Nerves connect directly to their target
Key characteristics of visceral (autonomic) PNS
-Connects to glands, involuntary muscles, walls of internal organs
-Neurons connect via a peripheral autonomic ganglion
Interneurons function and distribution
-Relay/integration
-Located in CNS
Motor (efferent) neuron function and distribution
-Visceral and somatic
-Cranial and spinal nerves
Sensory (afferent) neuron function and distribution
-Visceral and somatic
-Special sensory only in cranial nerves
-Both special and general sensory in spinal nerves
Function of sympathetic nervous system
Prepares for activity: fight or flight response
Function of parasympathetic nervous system
Homeostasis: rest & digest
Synapse type in CNS and parasympathetic nervous system
Cholinergic synapse
Synapse type in sympathetic nervous system
Adrenergic synapse
Three basic pathways involving PNS
-Reflexes
-Ascending pathways
-Descending pathways
Spinal nerve evolutionary origin
Innervation of pharyngeal slits
Function for which spinal nerves were originally evolved
Activating repeated muscle blocks for swimming in fish
Which cranial nerve comprises most of the parasympathetic nervous system?
Vagus nerve (cranial nerve X)
Categories of cranial nerves:
-Sensory nerves of the head
-Ventral cranial nerves
-Dorsal cranial nerves
Nerves of parasympathetic nervous system
-Vagus nerve
-Sacral spinal nerves
Nerves of sympathetic nervous system
Sympathetic chain (sympathetic trunk and paravertebral ganglia)
Evolution of cranial nerves
Slits for filter feeding -> slits to support gills -> muscles, vessels & nerves for gill function -> cranial muscles, nerves and aortic arches
Preganglionic neurotransmitter of parasympathetic nervous sytem
Acetylcholine
Preganglionic neurotransmitter of sympathetic nervous system
Acetylcholine
Postganglionic neurotransmitter of parasympathetic nervous system
Acetylcholine
Postganglionic neurotransmitter of sympathetic nervous system
Norepinephrine
Innovations in cranial nerve evolution
Tetrapods: vomeronasal organ and new glands
Amniotes: loss of lateral line system, decussation of optic nerve
Mammals&birds: cochlea developed
