1. Nerve Cells

2. Introduction
Two main types of cell in the nervous system: nerve cells and neuroglial cells.
Nerve cells or neurons are the basic functional unit in the CNS.
More than 15 billion nerve cells.
Neuroglial cells or glial cells support, protect and help in the repair of nerve cells.
App times as many glial cells to neuron cells
The brain of the adult human can sometimes compensate for damage quite well, by making new connections among surviving nerve cells (neurons). But it cannot repair itself, because it lacks the stem cells that would allow for neuronal regeneration. That, anyway, is what most neurobiologists firmly believed until quite recently.
Eriksson, Gage, et al (1999) published the startling news that the mature human brain does spawn neurons routinely in at least one site— the hippocampus, an area important to memory and learning.
Further recent (2007) research has shown that nanotechnology may pave way for nerve cell regeneration.
The four main functions of glial cells are to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy pathogens and remove dead neurons. They also modulate neurotransmission
Examples of Glial (or greek “glue”) cells include oligodendrocytes, astrocytes & schwann cells.

3. Nerve cells
Glial (support) cells

4. Neuron Their main role is to process and transmit information.
Through excitatory and inhibitory impulses, nerve cells serve all sensorimotor activities and higher mental functions, including attention, memory, thinking, language, etc.
Neurons are typically 4 to 100 micrometers in diameter.

5. Neurons Each neuron consists of: Cell body or soma
Contains the nucleus
The “brain” of the cell
Two types of processes:
Dendrites
The “input” side of a neuron
Axons
The “output” side of the neuron
The cell body and dendritic tree receive inputs from other neurons, and the axon transmits output signals to other nerve cells, muscles and glands.
Dendrites - Analogous to a sensory surface – many branches
Axons - Analogous to a cable carrying information (chemical or electrical) away from the cell body

6. Construction of Neuron

7. Nerve Cell Structure
Cell body: Two major components – Nucleus and cytoplasm.
Cytoplasm – contains microscopic organelles such as mitochondria, ribosomes, lysosomes, and golgi complexes.
Primary function is to metabolize protein for the maintenance, growth and viability of the cell
Cell bodies not only utilize and convert outside glucose to generate energy, but also manufacture their own protein.
This protein is conducted through microtubules through the axons.

8. Nerve Cell Structure Mitochondria - "cellular power plants“
Converts organic materials into energy in the form of ATP .
Lysosomes – Participates in intracellular digestion.
Ribosomes – Help in assembling protein.
Is like a factory that builds a protein from a set of genetic instructions
Golgi bodies/complexes – Responsible for protein secretion and functions as a central delivery system for the cell.
Adenosine triphosphate, the main energy storage and transfer molecule in the cell \
Ribosomes - takes information from the genetic code and uses it to piece together proteins, everything from hemoglobin to insulin Nobel prize in Chemistry goes to three scientists for creating highly detailed, three-dimensional, maps of the ribosome and all of its atoms.

9. Nerve Cell Structure
Nucleus: Controlling center of the cell and contains the genetic material, DNA (Deoxyribonucleic acid).
DNA is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms.
Often compared to a set of blueprints.
Nucleolus within the nucleus is the site of assembly of ribosomes and contain RNA which plays a role in protein synthesis.
Deoxyribonucleic acid, or DNA, is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules.
DNA contains the genetic information that allows all modern living things to function, grow and reproduce.
DNA was first isolated by the Swiss physician Friedrich Miescher who, in 1869, discovered a microscopic substance in the pus of discarded surgical bandages. As it resided in the nuclei of cells, he called it "nuclein".
Watson and Crick (1953) were the first to postulate the Double Helix structure of a DNA molecule with X-ray diffraction images taken by Rosalind Franklin
Double Helix structure of a DNA sequence

10. Nerve Cell Structure The Cell Membrane (Plasma Membrane)
The cell wall (or external cell boundary)
Maintains separation between intra- and extra-cellular fluids
Lined with the cell coat, which facilitates ion transport
Semipermeable membrane that allows some ions to pass while restricting the flow of others
While at rest, membrane allows potassium (K+) pass through (permeate) the membrane
But restricts the flow of (Na+)
Prepares the neuron for an action potential

11. Nerve Cell Structure
Dendrites are primarily afferent and carries information to the cell body from the synaptic sites.
Dendrites tend to be short and have many branches.
The branching of dendrites is known as arborization.
Increases the ‘reach’ of each individual neuron

12. Neurons in Hippocampus
Cell Body

13. Axon
Dendritic Surface

14. Nerve Cell Structure
Axons originate from a cone-shaped regions of the cell – Axon hillock
Is the part of the neuron that has the greatest density of voltage-dependent sodium channels.
And is the most easily-excited part of the neuron, and serves as the spike initiation zone for the axon.

15. Nerve Cell Structure
Axons are longer and are efferent projections Usually conducts impulses AWAY from the cell body
Axon + covering sheath = nerve fiber
Axons terminate by branching into a number of smaller filaments – Telodendria
Telodendria have synaptic knobs that contain various neurotransmitters at their end.

16. Nerve Cell Structure
The diameter and presence/absence of myelin sheath determines the speed of nerve conduction.
Myelin is an electrically insulating phospholipid (fatty) layer that surrounds the axons of many neurons.
Myelin sheath is formed in small segments that are interrupted by intervals – Nodes of Ranvier
During neural conduction, electricity jumps from one node to the next – Saltatory conduction
This accelerates nerve conduction up to 120 m/sec.

17. Neuron

18. Nerve Cell Structure Myelin sheath is an outgrowth of glial cells:
Schwann cells supply the myelin for the PNS neurons while oligodendrocytes supply it to those of the CNS.
Myelin growth begins during fetal period and continues till puberty – Myelogenesis
The growth rate and time span of myelogenesis is related to the development of sensori-motor and cognitive skills.
Damage to myelin sheath or its production in the CNS will impair nerve conduction such as in multiple sclerosis.
Multiple sclerosis is an autoimmune condition in which the immune system attacks the central nervous system, leading to demyelination. When parts of the myelin sheath is lost, oligodendrocytes attempt to replace it. However, in multiple sclerosis, it appears that the oligodendrocytes, themselves, are often destroyed thus compromising the repair process.

19. Nerve Cell Structure Synapse – connection point between neurons
Adult nervous system have about 100 to 500 trillion synapses.
Synapses have three parts – knob, cleft, and receptive site.
Knobs contain vesicles of neurotransmitters that are released during activation.
The released neurotransmitters commute across the synapse and stimulate the receptive site which can be a dendrite (axodendritic synapse), axons (axoaxonic synapse) or cell body (axosomatic synapse)
Receptive sites at adjacent postsynaptic neurons are chemically activated and generate electrical impulses that are carried to its body.
Each side of the cleft consists of a presynaptic or postsynaptic membrane

20. Nerve Bundles

21. Synapse

22. Classification of neuron types
Differ by shape, size, structure, and function.
Based on the number of processes:
Unipolar - Dendrite and axon emerging from same process. Are ‘T’ shaped. Ex., Spinal dorsal root ganglions
Bipolar - single axon and single dendrite on opposite ends of the soma. Ex., neurons in the retina, olfactory and auditory system.
Multipolar - more than two dendrites.
Mostly found in the CNS. Ex., Purkinje cells, pyramidal cells.

23. Neuron classification

24. Classification of neuron types
Based on axon length:
Golgi I - neurons with long-projecting (inches to feet) axonal processes. Ex., sensory and motor tracts
Golgi II - neurons whose axonal process projects locally. Ex., Interneurons that connect with other adjacent neurons
The longest axon of a spinal motor neuron can be over a meter long, reaching from the base of the spine to the toes

25. Pyramidal Cell

26. Pyramidal Cell “Forest”

27. Classification of Neurons
Based on function:
Afferent neurons convey information from tissues and organs into the central nervous system.
Efferent neurons transmit signals from the central nervous system to the effector cells.
Interneurons connect neurons within specific regions of the central nervous system.
Based on action on other neurons:
Excitatory neurons evoke excitation of their target neurons.
Inhibitory neurons evoke inhibition of their target neurons.
Inhibitory neurons are often interneurons.
Modulatory neurons evoke more complex effects on other neurons.

28. Convergent circuit
Lateral Inhibition
Divergent circuit
Reverberating circuit _ +
Neuronal circuits
Convergent circuit – Postsynaptic neurons receives information from a number of neurons of either same source or different sources.
Divergent circuit – Amplifies an impulse.
Lateral inhibition –Results in sharpening the response by inhibiting adjacent neurons.
Reverberating circuits – A self-propagating system that continues activation unless blocked by an external system.

29. Physiology - Nerve Conduction
Terminology
Synapse
Specialized points for communication between a neuron and another neuron, a muscle cell, or a gland
Presynaptic terminal
Formed by the axon end-projections of the neuron transmitting a signal
Postsynaptic terminal
Formed by the membrane region of the receiving cell
Synaptic cleft
The space between the two terminals
Neurotransmitters
Contained within vesicles in the presynaptic terminal
Used to transmit information across the synaptic cleft

30. Nerve Physiology
A neuron that is not transmitting a signal is said to be at its Resting State.
At this state, there is a difference between electrical charges on the outer and inner sides of the membrane.
How much electricity can the human body produce? – Not clear but presumably - a sleeping person can produce 81 watts, a soldier standing at ease can produce 121 watts.
Just like everywhere else, electricity travels on the surface of nerve axons.

31. Nerve Physiology
Resting membrane potential = ~ -70 mV
The inside of the neuron is negatively charged relative to the outside because of the large, negatively charged molecules in the cytoplasm.
Inside the cell – low in sodium (Na+) and high concentration of potassium (K+) cells.
However, there is some spontaneous passive exchange of ions across the membranes.
Sodium ions enter the membrane.
The greater the difference between positive and negative poles, or charges, the more powerful the flow of ions
Think of batteries with pos. and neg. poles
When voltage changes TOWARD zero, it is depolarization (excitatory)
When voltage changes AWAY FROM zero, hyperpolarization (inhibitory)
V (extracellular) – V (intracellular) = Battery Voltage

32. Resting potential & the Sodium-potassium pump
The sodium-potassium active pump maintains concentration gradients for both sodium and potassium ions.
ATP (Adenosine triphosphate) is the source of energy for this pump.
A large protein in the plasma membrane provides the doorway through which sodium and potassium ions can move.
Animation

33. Sodium-potassium pump
The addition of a phosphate group from ATP changes the shape of the protein and the sodium is expelled.
The phosphate is released and, as the protein returns to its former shape, two potassium ions are moved across the membrane.
Animation

34. Sodium-potassium pump

35. Nerve Excitability
Hyperpolarization – Cell interior becomes more negative.
Technically means ‘more polarized’
Depolarization – Cell interior becomes ‘less’ negative (i.e., changing towards positive charge)
Nerve excitability refers to the nerve cells response to external stimuli (i.e., chemical or temperature change, electrical pulse, or nerve tapping) and the conversion of this response into a nerve impulse or Action Potential.

36. Nerve Excitability
Action potential - Temporary reversal of the charges on the neuron cell surface membrane.
Results in the interior of cell becoming more positive – That is, the cell gets depolarized.
In most neural cells, to trigger an action potential, a change of at least 10 mV (i.e., change from -70 mV to -60 mV) is required.
Neuron Threshold value.
Not all stimuli are strong enough to reach this threshold value.
Also threshold potential value varies with type of cells.

37. Nerve Excitability
Initially, the local membrane depolarization caused by an excitatory stimulus causes some voltage-gated sodium channels in the neuron cell surface membrane to open.
This causes sodium ions to diffuse in through the channels.
And since they are positively charged, this begins a reversal in the potential difference across the membrane from negative-inside to positive-inside.

38. Action Potential
Hyperpolarization
Once a membrane potential of around +40 mV is reached, the voltage-sensitive gates of the sodium channels closes.
The further influx of sodium is prevented.
While this occurs, the voltage-sensitive activation gates on the potassium channels begin to open.
This results in a large outward movement of potassium ions.

39. Action Potential
This movement of positive charge causes a reversal of the membrane potential to negative-inside (i.e., back towards the large negative-inside resting potential) - Repolorization
However the large outward current of potassium ions through the voltage-gated potassium channels causes a temporary overshoot of the electrical gradient, with the inside of the neuron being even more negative relative to the outside (~ -80 to -90 mV) than the usual resting potential.
I.e., Results in the hyperpolarization of the cell.

40. Action Potential
This state is known as the absolute refractory period.
In the refractory state, the cell cannot fire another action potential until the membrane potential returns to its resting potential.
Animation
Animation 2
The action potentials of most nerves last 5-10 milliseconds.
Hyperpolarization

41. Action Potential or Nerve Conduction
In order for information to be transferred in the nervous system, the action potential, once generated, must travel down the axon.
The propagation of the action potential occurs because the influx of positive charge, during the rising phase, depolarizes the next segment of the membrane.
Rapidly it works its way down the axon to the presynaptical terminal, and initiates synaptic communication with another neuron or cell.

42. Action Potential or Nerve Conduction
Animation

43. Action Potential or Nerve Conduction
An action potential travels only in one direction.
It cannot turn back on itself because the membrane behind it is still refractory.
Also Action potentials propagate without decrement – Hence are called an "All or none" signal. 

44. Action Potential or Nerve Conduction
Aspects of the all-or-none law:
If the stimulus is too low (i.e., below threshold), there is no action potential - This is the "none" part.
If the stimulus is above a threshold the action potential is always the same size- it does not get larger for stronger stimuli - This is the “all” part
As the action potential travels along the axon it does not die out, but stays the same size.

45. Factors Influencing Action Potential Conduction Speed
Two factors –
Axon diameter: Action potentials propagate faster in axons of larger diameter because resistance to conduction is lower with larger diameters.
Myelination: Because all neurons cannot be gigantic to improve conduction speed, there is another mechanism to improve axonal conduction.

46. Factors Influencing Action Potential Conduction Speed
In myleinated axons, voltage-gated sodium channels are concentrated in the nodes of Ranvier.
Conduction velocity for ordinary nerve = ~1 meter/sec (depends upon diameter)
Conduction velocity for myelinated nerve = ~100 meters/sec
Conduction along these myelinated fibers is referred to as saltatory conduction.

47. Action Potential Conduction - Animation

48. Synapse
Neural synapses (also called chemical synapses) allow the neurons to form interconnected neural circuits.
The pre-synaptic neuron secretes the neurotransmitter at it bouton, which binds to post-synaptic receptors.

49. Physiological activities at the synapse
The release of neurotransmitter is triggered by the arrival of a nerve impulse or action potential and occurs through a rapid process known as exocytosis.
Within the pre-synaptic nerve terminal, vesicles containing neurotransmitters sit "docked" and ready at the synaptic membrane.

50. Physiological activities at the synapse
The arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels.
Calcium ions then trigger a biochemical reaction which results in vesicles fusing with the presynaptic-membrane and releasing their contents to the synaptic cleft.
Animation

51. Physiological activities at the synapse
Receptors on the opposite side of the synaptic gap bind to these neurotransmitter molecules and respond by the opening of nearby ion channels in the post-synaptic cell membrane.
This causes ions to rush in or out and changes the membrane potential of the postsynaptic cell.
The resulting change in voltage is called a postsynaptic potential.

52. Review Resting potential and Action potential- Animation
Synapse – Animation
Neurons - How they work video

53. Post-Synapse
Postsynaptic potentials are changes in the membrane potential of the postsynaptic neuron.
Postsynaptic potentials are graded potentials (unlike the “all or none” type of the action potentials).
The amount of neurotransmitter released from the presynaptic terminal is directly related to the total number of action potentials per unit time reaching the terminal.
An increase in either the strength of a stimulus or the duration of a stimulus to the presynaptic cell also results in the release of greater quantities of neurotransmitter.

54. Post-Synapse
The neurotransmitters bind to receptors on the postsynaptic neuron by having a particular shape or structure (kind of like the way a key fits into certain locks).
Typically these receptors react to the binding of neurotransmitters by opening or closing an ion channel thereby allowing ions to enter or leave the cell.
It is these ions that alter the membrane potential of the postsynaptic membrane/neuron.

55. Postsynaptic Potentials
Remember, the neighboring neurons also have a resting potential of about -70mV.
There are two kinds of postsynaptic potentials.
Excitatory postsynaptic potential (EPSP).
If the release of Neurotransmitter across synapse produces excitatory (depolarizing effect)
Main agent is ACh (Acetylcholine) which facilitates many muscle movements
Inhibitory postsynaptic potential (IPSP).
If the release of Neurotransmitter across synapse produces inhibitory (hyperpolarizing effect)
Main agent is gamma-amniobutyric acid (GABA) which is important in sensory systems and for fine muscle control
EPSP and IPSP
Excitatory or inhibitory post-synaptic potential
Release of Neurotransmitter across synapse produces excitatory (depolarizing effect)
Main agent is ACh (Acetylcholine) which facilitates many muscle movements
Or inhibitory (hyperpolarizing effect)
Main agent is gamma-amniobutyric acid (GABA) which is important in sensory systems and for fine muscle control

56. Postsynaptic Potentials
EPSPs and IPSPs are transient changes in the membrane potential.
EPSPs from a single synapse are generally far too small to trigger a response in the postsynaptic neuron.
However, a neuron typically receives synaptic inputs from about 10,000 other neurons, so the combined activity can cause large fluctuations in membrane potential.
If the postsynaptic cell is sufficiently depolarized, an action potential will occur in this postsynaptic neuron.
Over-stimulation of the limbic system & RAS results in the ADHD symptoms of over-arousal and hyperactivity. Norepinephrine and dopamine are neurotransmitters which control attention and focus in the brain. Increased arousal of these neurotransmitters results in hyper-vigilance and restricts the development of neural
connections which strengthens the process of receiving information to the brain. Medications usually used to treat ADHD improve the availability in the synapse of two neurotransmitters, dopamine and norepinephrine.

57. Central Auditory Pathway - Auditory Nerve and Ascending Auditory Pathway

58. Introduction
The neural code originating at the base of the hair cells are conducted to the auditory cortex by the central auditory pathway.
The central auditory system begins from the CN VIII cell bodies lying in the spiral ganglion.

59. Through the central auditory pathway, the auditory system sends its information to different parts of the brain specifically to extract the sound cues out of the electrical message brought by the nerves of hearing. This system begins as the nerve of hearing enters the brainstem. From here, the neural pathway makes its way up to the cerebral cortex at the temporal lobe of the brain along the way switching back and forth from each side of the brainstem with neurons multiplying in number at each relay station along the circuit. Right ear information is directed to the left temporal lobe, and left ear information goes to the right temporal lobe. In addition, there is a transfer of information from one side of the brain to the other. In most people, the left side of the brain processes speech and other complex language functions, whereas tonal stimuli and music are deciphered by the right side of the brain.

60. Midsagittal view of the CNS
Spiral gaglion and nerve definition for test.

61. Introduction
The central auditory pathway consists of many ‘stations’ wherein different kinds of processing takes place.
The exact mechanisms of these central auditory processes are still poorly understood.

62. Central Auditory Pathway
MGB IC LL CN
SOC
Aud.Nerve

63. Tract- axon material in the CNS…
Nucleus – cell bodies in CNS
Once you get into the CNS the number of synapses significantly increases.

64. The Auditory Nerve
Nerve fibers pass from the modiolus of the cochlea through the internal auditory canal.
Internal auditory canal begins at the modiolus and terminates at the base of the brain (brain-stem).
It also encloses the vestibular portion of the CN VIII.
Need to know:
CN – cholear nuclues
SOC – superior olivary complex
Nll- Nuclei of the lateral leminiscus
IC-
MGB

65. The Auditory Nerve Also known as the Vestibulo-cochlear nerve
The auditory nerve is also tonotopically organized with the nerves serving the basal cochlea (high freq) forming the outer portion and those from the apical (low freq), the center.

66. The Auditory Nerve
The auditory nerve extends 17 to 19 mm beyond the internal auditory canal, where it attaches to the brainstem at the cerebellopontine angle.
Junction of the cerebellum, medulla, and pons in the brainstem.
At this level, the auditory and vestibular portions separate.
The auditory nerve terminates at the cochlear nuclei.

67. The Auditory Nerve
The VIII CN is primarily a sensory nerve (afferent nerve) but also contains a limited no of efferent fibers.
The efferent or descending pathway is also known as the olivo-cochlear tract or Rasmussen’s bundle.
The exact function of the auditory efferent system is still poorly understood.

68. Auditory Nerve

69. Cochlear Nuclei
The VIII CN enters the brain stem at the cochlear nuclei on the ipsilateral (same) side of the upper medulla and pons.
The cochlear nucleus is the first processing station in the central auditory system

70. Cochlear Nuclei
The cochlear nuclei preserves the information coded at the cochlea and conveys it to the next ‘station’ - the Superior Olivary Complex (SOC).
Also some important decoding of the basic signal occurs: duration, intensity and frequency processing

71. Cochlear Nuclei CN

72. Superior Olivary Complex
The SOC is an important relay station because it is the first structure in the pathway that receives binaural information.
The nerve pathway from one cochlea ‘decussates’ or crossovers at this level.
The SOC is believed to be the main processing center of binaural information such as localization.

73. Superior Olivary Complex
Moreover, The SOC is an important center that mediates the middle ear reflexes (tensor tympani and stapedial reflexes).

74. SOC
SOC
Know where the soc is.

75. Lateral Lemniscus (LL)
The LL is primarily a tract of axons ascending the brainstem at the pons.
All divisions are tonotopically organized.
No definite processing takes place at this nuclei.

76. Inferior Colliculus (IC)
Is an important processing center located in the midbrain.
Receives afferent information from both superior olivary complexes.
The IC is involved in integration and routing of multi-modal sensory perception.

77. Inferior Colliculus (IC)
Receives visual and touch information apart from auditory information.
It is involved in the startle reflex and vestibulo-ocular (“doll’s eye reflex) reflexes.
It also modifies activity in regions of the brain responsible for attention and learning.

78. Inferior Colliculus (IC)
IC has neural units that are sensitive to spectral changes in the sound.
Hence is believed to be the first center wherein phonemes and intonations are probably perceived.

79. Inferior Colliculus IC

80. Medial Geniculate Body (MGB)
Is the last sub-cortical relay station before the cortex.
Is located in the midbrain.
After the MGB, the auditory fibers fan out as the auditory radiations and then ascend to the cortex.
No decussations or crossovers occur at this level.

81. Medial Geniculate Body
MGB

82. The Auditory Cortex
The areas of auditory reception are in the temporal lobes on both sides of the auditory cortex in an area called the superior temporal gyrus or Heschl’s gyrus.
Auditory Cortex lies in the Sylvian Fissure of the Temporal Lobe.
Broadmanns areas 41 & 42
Primary auditory cortex.
In human, the primary auditory cortex (3) is located in the temporal area (2) within the lateral sulcus (1).

83. Lobes of the Cortex

84. The Auditory Cortex Tonotopicity again exists in the auditory cortex.
The auditory cortex relays auditory information to other cortical areas such as speech areas (Brocas and Wernickes), parietal lobe and other parts of the temporal lobe.

85. Functional Areas of the Cortex

86. Auditory Cortex

87. CANS

88. Hallmarks of the Auditory CNS
Decussations and bilateral projections occur starting from neurons in the cochlear nuclei.
This property of early bilateral projections is clinically important because the bilateral redundancy in the ascending pathways seldom, if ever results in monaural hearing loss.
Multiple parallel pathways that appear to underlie our capacity for perceiving different aspects of sound stimuli.
Tonotopicity - Spatially ordered frequency representations are maintained through most structures/levels in the CAP.

89. CAP
The sence of smell trigers memory more than any other thing. Next is hearing.
Corpus Calosum- is where the two hemispheres are joined together.

90. CAP
The first relay of the primary auditory pathway occurs in the cochlear nuclei in the brain stem which received type I spiral ganglion axons (auditory nerve). At this level an important decodoing of the basic signal occurs: duration, intensity and frequency.
8th nerve- cochleor nuclei.
Superior olivary complex is the lowest level of the brain stem that is recieveing inveration by both ears. So basically at a ver low section of the brain stem it is already combing the sound from both ears.
States of arousal are stimulated by the reticular activating system.

91. CAP Reweighting of synaptic activity is the def of learning.
Decussation is when fibers cross the midline of the brain stem.
SOC soperior olivary complex – the area where the nerve fibers pass through and synapse. The greenish/yellow portion of the diagram.
Axon in the CNS are called…
Primary conduit in the auditory pathway is the lateral laminiscis.
There is an efarrent control over an afferent system because you can prime yourself to be ready to learn.
Heschels gyrus- ridge in the brain.
Sulcus is the the groove.
The whole pathway is tonitiopic like the cochlea.

92. Remember…..
CNS LIMCA
Cues for localization- Interaural level difference vrs interaural time difference.
ITD- sound takes llong to reach ear. Low frequencies.
ILD – Head shadows sound going to far ear. High frequencyies